Repair and Diagnosis of Problems with Your Imperial's Gauges


Imperial Home Page -> Repair -> Electrical System ->Gauges

How To Test Whether Your Gas Gauge or Sender Unit Is Inoperable- by Dick:

1) Disconnect the battery 

2) Disconnect the wire that goes from the car to the sending unit - at the tank. 

3) Ground the wire to the chassis 

4) Re-connect the battery and turn on the key. If the tank indication is 3/4 the gauge is bad. If the indication is full the sender is bad. 

5) To fix the gauge, remove and replace 

6) To fix the sender, remove it and CAREFULLY bend the arm down so as to elevate the float and raise the reading. If all else fails, read the book, although it will probably tell you the same thing. 

BTW, it does not matter the model, all old Mopars are likely to use a similar setup. 

How To Test The Accuracy of Your Oil Pressure Gauge - by Dick:

If you want to see how fast your oil pressure is really rising, get a mechanical (actually, hydro-mechanical) gauge and temporarily install it in the same location as your electrical gauge sending unit. I have one I use for testing oil pressure and pumps on freshly rebuilt but not yet operated engines. I have taken such a gauge and connected it to an 18 inch piece of grease gun extension hose, which has the proper 1/8 pipe thread, so I can simply screw in the temporary gauge and watch what happens when I run the oil pump. In my experience, the pressure comes up to full relief valve setting within one rotation of the oil pump shaft.

How To Test A Temperature Gauge - by Dick:

Here's how to check it:  (You could check in your shop manual to be sure about the colors etc.) 

1. get a 12 volt battery and connect the negative post to the case of the dash unit. 

2. connect the positive post to the "I" terminal (Probably has a black wire on it). 

3. Take your VOM or test light and connect to the "5 volt regulator output" which will probably have an "A" marked by it and connect to a wire (can't give you a color, it's a printed circuit on the 68) which goes directly to the other two sensor type gauges (not the ammeter or generator or charging indicator or whatever its called on a 61) and verify that you see a pulsating voltage bouncing, every second or so, from near nothing to near 12 volts. If you do, regulator is alive and kicking. (Ground your test device to the case, use the positive probe on the "A" terminal.) 

4. Now find a temp sender that you know to be functional (you can check it with your VOM, which I hope you have, by measuring the resistance from its little brass threaded mounting to its wire terminal. You should read in the hundreds of ohms with it cold (typically 240 ohms) and in the 10's of ohms when you put it in a pot of boiling water (typically 10 ohms). 

5. Now that you know you have a good temp sender, connect it to the "S" terminal on the gauge (Probably a violet wire), ground the outside of the temp sender to the negative post of the battery, and see if the gauge indication is sort of correct. Got the boiling water still handy? 

6. There is an alternative method. Install it and hope. Your choice.

Response Time of Electrically Operated Gauges -by Dick:

All the electrical gauges on our cars are operated by a bi-metallic spring that is heated by a very fine wire wound around the spring. This type of gauge cannot, by its nature, respond quickly. The only type of oil pressure gauge that can respond quickly is the old copper tube operated type, as used in most cars until the late 40's. 

If you want to see an example of how fast a gauge can respond, note your temp gauge reading before you turn off your engine when it is thoroughly warm. Then, after the gauge returns to the cold peg, but before the engine has a chance to cool at all (say within the next 2 or 3 minutes, for example), turn on the key again, but do not start the engine, and watch the movement of the indicating needle. You will see it move up very slowly, with perhaps a noticeable surging motion (caused by the cycling of the gauge regulator) until it reaches the correct reading. That is the response time of your gauge when presented with a sensor input that is already at its steady state - in other words, if your oil pressure gauge comes up at about the same rate, you aren't learning anything about how fast the oil pressure is coming up by watching the gauge. 

If you want to see how fast your oil pressure is really rising, get a mechanical (actually, hydro-mechanical) gauge and temporarily install it in the same location as your electrical gauge sending unit. I have one I use for testing oil pressure and pumps on freshly rebuilt but not yet operated engines. I have taken such a gauge and connected it to an 18 inch piece of grease gun extension hose, which has the proper 1/8 pipe thread, so I can simply screw in the temporary gauge and watch what happens when I run the oil pump. In my experience, the pressure comes up to full relief valve setting within one rotation of the oil pump shaft. 

On a really worn engine, you can often hear the main bearings knock during the first rotation of the engine when it is started warm, if it starts on the very first turn of the key - the noise quits when the oil pressure comes up, usually within less than a second. When you hear this noise, start saving your pennies in a BIG jar.

Question from Tony:

How can we tell if a gauge is any good?

Reply from Dave:

You can use a 12 volt power supply on the power pin of the gauge assembly and clip the negative anywhere on the case. Now put an analog (that means one with a dial and pointer) volt meter, or a 12 volt bulb on the output pin and look for a pulsing 12 volts. If it's there, then the regulator section is OK. If the regulator checks out, then run a jumper from the temp gauge signal pin to the case (leave the power supply running) and if the gauge goes full-scale HOT, then the gauge is working. That's how you'll know. And if you've got one that works, give me a price and I'll buy it!

Question from Norman:

I noticed the other day that when I move the power seat or put the windows up or down my amp gauge swings well into the charge side. If I turn on the headlights, brake lights, turn signals, or blower motor it acts like I would expect by going slightly to the discharge side or at least less into the charge side. Has anyone seen this before? Is it something I should worry about? Where would I start to diagnose the problem?

Reply from Dick:

It's not a problem. The really heavy current loads on a car are often routed to bypass the amp meter. What you are seeing is the alternator providing the replacement current to keep the battery charged while the humongous load is going on. If you do this with the engine off, you'll note the "problem" does not occur. This is because the alternator is not running, and the current you are using is not being replaced (until later, when you do start the engine, at which time it will charge the battery a little extra to make up for the electrons you stole from it while it was asleep.)

Question from Bob:

Is it possible to build a shunt or jumper across the back of the amp gauge to take some of the load (read heat) off of the gauge itself? Would you, should you put a fuse in the shunt/jumper to help prevent a harness meltdown since the gauge kind of serves that purpose now? I have always thought this design feature of a Chrysler product, of running the entire charging/elect. system through the gauge was a poor idea and has left many a person stranded and ticked off (me included) Just an idea, comments?

Reply from Joe:

Actually the shunt is built into the ammeter. If you look closely, you will see that a fairly heavy piece of metal connects between the two posts of the ammeter. This is one reason they are as durable as they are. Some of the designs, however, have the posts bonded to the metal shunt by staking the posts against the shunt - this appears like a small spur of metal spread out from the post mashed down against the shunt metal. Sometimes there is also a piece of insulating material between the two and there is only a pressure contact between a shank on the post and the shunt. If there is any overheating at all for any reason, the fiber insulating material used chars and begins to fall away from the area leaving a loose connection which causes even more overheating of the connections and erratic operation of the gauge. Sometimes these can be repaired using nuts of the correct size and thread along with suitable "star washers" to re-establish a good connection between the shunt metal and the posts (after first cleaning away the remaining charred insulation material). I was able to repair the ammeter gauge on a Dodge pickup this year for my son this way. Be prepared to make front to back depth adjustments if necessary to the dash area that receives the gauge if the extra nuts push the gauge too far forward when installed in the instrument cluster. How to do that is left to your own investigation and imagination. 

One common cause of problems to start with is people who mistakenly install a heavier alternator for the original, thus forcing heavier current through the original gauge than it is designed to handle. My son's pickup suffered from this. The original alternator was a 75 amp unit which had been replaced with a 120 amp unit. The original ammeter circuit fed the ammeter leads through a bulkhead connector to the ammeter and back through to charge the battery. The contacts in the bulkhead connector were not designed to handle 120 amps. Even the 75 amps originally intended may have been marginal! The heavy current charred the contacts, started corrosion of the contacts which made the problem even worse and eventually almost ignited the plastic insulation of the bulkhead connector. Examination of the service manual showed that although the same ammeter was used for both applications (regular duty and heavy duty alternators) units produced with the heavy duty alternator routed wires through a feed-through grommet in the firewall instead of going through a bulkhead connector. They knew that the connector could have no hope of holding up under that kind of current. We had to modify the engine compartment wiring from the alternator all the way through a newly installed feed through grommet and back into the firewall to the battery etc. to cure the problem along with repairing the ammeter as described previously. 

The average mechanic would never have understood the issues involved. Thank goodness for my electrical engineering training! Most mechanics are no help on issues like this. Check your car to see if it has had a larger alternator installed than originally called for. You could have the same or similar problems.

Question from Drex (1954):

My temp gauge quit working in my 54 Imp.  I am under the impression the entire gauge must be replaced. Is this true?  Can the old one be repaired?  I really don't want to mangle anything trying to get the old one out.  Can anybody give me some insight into this problem.

Reply from Dick:

I am not familiar with 54's, so some of this will seem like stupid questions. First, is the temp gauge a "Bourdon tube" type, or does it have an electrical sending device? To distinguish these, if you don't already know the answer, find the sending device. If it is the former, it will have a small copper tube attached to it, ending at the dash indicator. If it is electrical, the sender will be connected with a wire, of course. If it is the tube type, you will have to remove the sender from the block and the indicator from the dash WITHOUT DISCONNECTING THEM FROM EACH OTHER and send them off for repair to one of the services advertising temperature gauge repair in Hemmings. I have always used Dick Evans "the temperature gauge guy", but I suppose there are others. If it is electrical, momentarily ground the sender end of the wire while someone watches the indicator (key on, of course). If the dash indicator is all right, the needle will travel up the scale in pulsating jerky motions about one surge per second. If this happens, the dash indicator is probably OK, and the gauge regulator is also OK. The problem, in this case, is most likely a failed sending unit. If you have access to a VOM, check the resistance of the sending unit terminal to ground, with no wires connected to it. If it has failed, it will probably read a very high resistance (over 1000 OHMS), and if it is OK, it will read around 100 ohms, give or take a factor of two or so, and depending on the temperature of the engine. By the way, if your fuel gauge is working OK, the gauge regulator has to be good. If grounding the sender wire at the engine end does not cause the indicator to move, you will have to locate the dash end of the same wire, and repeat the test. If it moves the needle now, of course the problem is in the wire itself. If grounding the wire right at the dash indicator terminal does not make the indicator respond, you either have a failed indicator or a failed connection from the gauge power supply, AKA Gauge regulator. In either case, you are going to have to crawl under the dash and investigate, sorry. If the indicator itself has failed, it is most likely not repairable, you will have to locate a replacement indicator. By the way, this is one of the more frustrating things about converting a car to 12 volts, the indicators are very delicate, easily ruined by supplying them with the higher voltage, and almost always unrepairable once damaged in this way. Often, if a car has even been jump started with a 12 volt battery (I know, it really makes the starter spin, and will sometimes be the only way to get a really tired engine to start), the dash indicators will be ruined and you have a real problem on your hands.

Question from Robert (1954):

Anyone happen to know what the resistance range should be for my fuel gauge?

Reply from Dick:

The fuel gauge sender should vary from around 10 Ohms to around 70 Ohms, with the larger resistance occurring at empty. A plus or minus 30% variation is not significant for this type of gauge. You may find it described in the "fuel" section of the manual, or perhaps in the "instruments" section. These devices that cross boundaries between major sub-systems sometimes get sorted into weird locations in the manuals.

Question from John (1956):

My '56 gas gauge goes to full when the car is full, but when it gets down to about half a tank or lower it just bounces and jiggles around the half way mark.  Any ideas?

Reply from Mark:

Yeah, there's probably something amiss at the sending unit, maybe a bit of dirt or corrosion. Thankfully, this isn't such a bad thing as the sending unit is pretty easy to service. Under the carpet in the floor of the trunk you'll find a rubber dome about 4 inches in diameter. It's going to be right about the middle of the floor, and will have a wire running into it. Pry it up. Under that you'll find the sending unit. Remove the wire that's held down by a Phillips screw. Then remove the lock ring that holds the sending unit itself by using a flat-bladed screwdriver and a light hammer, tapping at the four tangs that stick up from the ring. Work around the ring, tapping on one tab a couple of times, then the one opposite. It will turn 90 degrees, then be free to lift off. You can then remove the sending unit. It's basically a rheostat that's operated by an arm. On one end of the arm are a couple of pieces of cork. Does this arm move it's full range freely? The other end of the arm goes into a domed metal housing that's held on by a pointy tang. Bending this tang allows the housing to be removed. You'll see that the arm goes through a pivot point, and is connected to a brass finger on the other side. This finger moves along a cone that is wound with a very fine red wire. The red wire is gong to be worn to a shiny silver where the finger has been rubbing it. This is normal. Make sure the brass finger is in contact with the cone throughout the entire travel of the arm (carefully bend it if you need to), and that the contact area between the arm and the cone is clean. (Use a rubber pencil eraser to clean it. This is a delicate winding, so use care!) If the arm doesn't move it's full range, or hangs up, there is dirt in the pivot point. Clean it out using an oily spray, like WD-40. Put it all back together, and that should do it. The sending unit will go back onto the tank only one way. There is a tang on it that keys it to a notch in the tank opening.

Question from Clay (1960):

I am having a rather strange problem with the gages on my '60 Custom. It seems that the gas and temperature gauges have developed a mind of their own . The temperture gauge will fluctuate between what looks to be a normal temp reading, to 3/4 hot . Then it will swing back to what I consider a normal reading. The gas gauge that worked last fall has now stopped working. It will sit at 1/8 full no matter the amount in the tank. The weird thing is that every so often the indicator will swing over to 1/2 a tank, while the temperature gauge will simultaneously move toward cold . Would anyone know what is causing these gauges to act this way?

Reply from John:

I think its either a poor ground or the gauge with the voltage limiter is going bad. Mine does this occasionally & if I wiggle the chrome trim bezel around the gauge cluster, it usually returns to normal.

Question from Dietmar (1960):

I installed new gauges on my car.  Now, they don't move, only the ammeter. I have 6 volts there - system is twelve - but not constant.  Any ideas?

Reply from Dick:

I do not have any experience with the 1960 models, but your 6 volts available at the gauge sounds right to me. It should actually pulsate, but average around 5 to 6 volts. This is your gauge regulator at work, and it sounds like it is OK. If your gauges are not reading anything (the ammeter is a special case, it does not use the regulated 6 volts, so the fact that it is working isn't telling you very much), the problem must be either in the grounding of the gauge or perhaps the complete gauge cluster assembly to the metal anchoring points on the dashboard. Are you sure you have good metal to metal contact where everything is bolted together? If this is OK too, then you have to start tracing wires. Something is not hooked up, and if all 3 gauges are dead, it sounds like it is on the gauge regulator side of the circuit. If you have a wiring diagram for the car, just get out your voltmeter and follow the wires, starting from the gauge regulator, and making sure there is no voltage on the metal part of any gauge (in other words that it is properly grounded). Hope this is clear.

Question from Luke (1960):

Has anyone replaced the mechanical voltage regulator inside the temperature gauge to an electronic one? My Fuel just reads 1/4 no matter how full the tank is. So the problem may well be faulty Voltage regulator.


From Dick:

If your temp and oil gauges work correctly, there is nothing wrong with your gauge regulator. It sounds to me like your tank sender is in trouble. Have you pulled it out and swung the arm through it's range to see if it makes the dash unit respond?

The mechanical gauge regulator is pretty close to a bulletproof design. I have 60 year old cars in which it works fine, and always has. I think this is pretty typical.

From Norm:

Ground the wire that goes to the sending unit on the gas tank. Turn the ignition on. If the gauge reads full, your problem is the sending unit, not the gauge.

Question from Kerry (1960):

When my 1960 starts, both the oil pressure AND the temp gauges go to max. I put a capillary oil pressure gauge on it and when started it and it pops right to 50 lbs so the oil pressure is ok.  Any ideas on how to fix this?

Reply from Dick:

The gauges pegging when you turn on the key probably (remember, I never say "definitely") indicate that the gauge regulator is stuck in the "on" position. Verify that you have a pulsating 12 volts at any of the sender wires (with the wire disconnected). If you do, I'm wrong, but if you don't turn off the key before you cook the dash instruments!

If you see a solid 12 volts at the sender end of a gauge wire, your gauge regulator is stuck, and you must either replace it or inspect it's mounting for a good ground to the chassis. If the ground is bad, this will produce the same symptom. I repeat, don't let this situation persist, or you'll be looking for 3 new dash gauge units!

The gauge regulators were hidden in various places in various years. One can always ignore the factory gauge regulators and install a separate one anywhere behind the dash, just follow the original FSM for hookup. NAPA has an exact electrical equivalent, I believe it is their IR-9. They call it an "instrument regulator", some also call this device a "voltage limiter".

Question from Chris (1960):

I have just started having this problem with my New Yorker - gas gauge reads beyond Full all the time now. Is it dangerous to operate the car with this condition (dash fire?), or is it something that can be fixed at one's leisure?

Reply from Dick:

The only danger I would worry about would be permanent damage to the dash indicator. To prevent this, disconnect the sender wire at the dash indicator end, until you have time to troubleshoot the short. Actually, it might be pretty easy to find, as usually the wire from the tank unit is rubbing on the frame near the tank. Why don't you inspect that first, you might find the problem right away. If you can't do that, then disconnect the wire at the dash unit before you operate the car again.

The reason this might damage the indicator is that these are basically heat operated gauges, with a bi-metallic strip which bends to move the pointer. The system is designed to register full scale when the sender rheostat is at 10 ohms resistance or so (this is not a critical number), but that is the design maximum for the heat generated within the indicator. A dead short, or zero ohms, drives the pointer beyond full scale by overheating the bi-metallic strip. With a persistent short, you could actually fry the heater coil wires that are wrapped around the strip. This is a permanent failure, when this happens, unless you are very skilled with tiny wires, and have a supply of extremely small nichrome wire to use for repairs. Much better to prevent the damage when you can.

Question from Mike (1961):

The gas gauge doesn't work. Does anyone know how we can fix it?


From Dick:

The gas gauge works by monitoring the current flowing from the dash back to the tank sending unit, and then to ground at the tank. The usual symptom is that the gauge reads zero all the time. If this is your problem, disconnect the wire that goes into the tank (Probably have to do this from under the car, unless there is an access plate through the trunk floor. Lift up the mat and look there first, or I'm sure another '61 owner will know.) Anyway, take this disconnected wire and run a temporary clip lead from it to a good ground, like the bumper. Now turn on your key and the gas gauge should show a full tank. If it does, you have localized the problem to either a missing ground wire from the tank to the car frame, or a failed sending unit. If you reconnect the wire to the sending unit, and run a temporary ground wire from the tank to the bumper, and it does not make the gauge work, your sending unit is bad. If your symptom is something other than reading empty all the time, or if grounding the sender wire does not bring the gauge to full, hit me again and we'll pursue this critter further. By the way, I assume your temp. and oil pressure gauges are working correctly? If not, that's a whole different kettle of fish.

From John:

Crawl under the car and disconnect the gas gauge wire connection at the sending unit at the front of the tank. Clean up the connector contacts with a piece of fine sandpaper wrapped around the tip of a small bladed screwdriver. Sometimes the contacts are just dirty or they've worked loose over the last thirty-some years. If no go then jump the gauge side wire to a good clean ground on the chassis. Now get in the car and turn the ignition switch on for a few seconds. If the gauge jumps to full the problem is in the sending unit and you will have to drop the tank for a repair. To confirm, if you have an ohmmeter, measure the resistance from the sending unit connector to chassis ground. The resistance should be a few hundred ohms at the most even if the tank is empty. If the gauge stayed at empty the problem is the gauge or wiring.

Question from Jeff (1961 -1962 interchange):

Does anyone know if the temperature gauges are the same part number in 61/62 Imperials? I found a NOS Temp Gauge for a 1961 Imperial....I need to make sure it is the same for 62.


From Joe:

The color of the gauge is different where the black is on the gauge face. It is a little more gray on a 62.

From John:

'61 & '62 are the same. The '63 is also the same gauge with a gray background instead of black.

From Jay:

The four needle-type gauges in the '61 & '62 Imperial dash have black backgrounds. In '63 the Imperial used the same gauges and cluster but with a gray background.

The '61 & '62 gauges and instrument cluster are fully interchangeable. Functionally, the '63 gauges will work in the two previous year models.

Question from Thomas (1962):

This is the situation. I have a new regulator, all electrical connections in the engine compartment have been cleaned, the battery seems to be OK (it's one of those with the green "light" indicator) and the dash gauge has been checked out. Now, this is what happens with the gauge. If the car has sat for a while and the engine is started, the gauge reads all the way to charge and then settles back down after a while. When I use the turn signals the gauge flickers to the charge side in time with the turn signals. When I run the windows up or down the ammeter gauge jumps over to charge until I release the window button. Do I need a new alternator or a new battery or both? Is either one not putting out enough amperage?


From Dick:

This situation comes up often on these cars. Your ammeter is behaving correctly, excepting only that it is reacting too strongly to the variations in charge rate that occur during normal operation. If you search the archives for the discussion on replacing ammeter shunts, you'll see what to do to correct this. Briefly, you connect about 1 foot of # 18 wire from one terminal to the other on the ammeter. On your broken return tab on the TS switch, you should check out the replacement kits offered by NAPA stores. They make one for the later cars with cornering lights, and possibly they have one for your car. They are a real bear to install, but they do work.

From Peter:

Your electrical system is behaving exactly as it should. No need to change any parts.

From John:

Just a common occurrence with Mopar electrical systems. My 300 does it too. It would be a problem if the ammeter showed a discharge in all of the aforementioned applications.

From Adam:

My '64 Crown was behaving the same way, most Mopars of our vintage did. The dancing alt gauge and flashing headlights drove me nuts. It's the mechanical voltage regulator. Then Dick Benjamin told me NAPA sells an electronic voltage regulator to replace the OEM mechanical one. It's a little pricey ($53 or so) and they had to order it. Boy what a difference. Gauge is pretty steady and almost no flashing of headlights. Well worth the expense to me.

Question from Bill (1963):

I purchased one of the few remaining '63 Crown convertibles about 4 weeks ago. It had charging problems. For peace of mind I decided to replace just about everything related. I first had the alternator tested. It was not giving a full charge. Replaced it and still had a charging problem. Then I replaced the battery and cables. After replacing the voltage regulator, I noticed the stock amp gauge moved to where it should be in the charging position. Now when I turn the headlights on, I notice the gauge bounces around in the charging position sporadically. Does anyone know what this is? Am I damaging the system?


From Paul:

I know what this is, and it took me years to find out. The bouncing amp gauge and flickering headlights are actually caused by one or two bad connections in the wiring harness where the connections go through the firewall. I think all '62s have this problem, probably '63s, and maybe all early alternator equipped Imperials.  The problem exists in the wires which detour to the key switch en route from the alternator to the voltage regulator. The low voltage of the field wire causes it to fall prey to oxidation in the connections through the firewall creating resistance. That results in an intermittent voltage or even a spark occurring in the firewall connection. It is not the voltage regulator, it is the wiring. But beyond that, this condition destroys the diodes or rectifiers in the alternator. One by one they go, even if the alternator is new. As each diode goes, the output of the alternator is reduced to nothing. The cure for this problem is to disconnect the firewall connections of the wiring harness and thoroughly clean the contacts of all oxidation. Replacement of the alternator may also be necessary. Check the circuits for resistance upon reconnection.

From Demetrios:

I have a similar problem with my 68 LeBaron. Now, my problem is not that the lights go off, just that the voltage appears to suddenly change. The "problem" appeared when I replaced the (failed) solid state voltage regulator with a standard one that was sitting on the trunk of my sedan for years (probably the original in the sedan). Dick B. had told me that this behavior is normal of the old regulators, since they have only 3 or 4 charging settings as opposed to infinite charging settings of the modern regulators. It has been like that for over 6 months now, no charging problems. I think though that I have a 35 amp alternator (original was 67 amps), and if I run AC too long at low speeds, the battery seems to lose charge faster that can be recharged (so I have to turn off the AC a bit). I doubt that its the regulator fault though.

From Chris:

It depends on what kind of voltage regulator you have. Did you replace it with an OEM style relay driven regulator, or did you replace it with a solid state type? If it is the relay type, chances are it needs (the relays) to be adjusted. One of the relays may be sticking, thus not being able to excite the field winding (rotor) in your alternator under load. If it is the solid state type, your problem is most likely the reference it is getting for regulation. It should be the + terminal of the battery. (actually, this applies to both styles) A stretch may be the fact that one of your new battery cables needs a connection tightened or cleaned if it's on a corroded or rusted surface. The headlights put a fairly good load on the charging system, and a poor connection can make things heat up and act crazy.

You may want to hold on to the regulator you replaced. It probably still works well. Just remember to never remove a battery terminal while a car is running. It is the quickest way to destroy a regulator, or derate one of the diodes in the alternator. This condition is called a load dump, and it generates a surge of 40 and up to 60V on your entire electrical system. Usually the battery winds up getting the punch, and it can be very dangerous. (The battery in a car's electrical system is also the filter capacitor that maintains a very constant DC level - not to be confused with the RF noise from plugs firing, and the ignition coil which has high frequency components and requires a different kind of filtering).

Question from Bob (1963):

OK---- fully totally rebuilt engine, newly rebuilt Alternator, new voltage regulator....system is charging, but....

on a normal acceleration the alternator/battery gauge indicates a normal charge level for about 10 to 15 seconds, then starts to quiver/bounce wildly from normal to full charge (from top center of the gauge to the far right) frantically back and forth.

No other indications of any problems...... any ideas on what is causing this?

At an idle with the headlights on, in gear and brake applied, the gauge indicates a slight discharge.


From John:

Loose connections at alternator or regulator. More probable is defective regulator/alternator. The regulator points are out of adjustment. Worse case short in a circuit. With the lights on, similar to what you were doing, rev the engine and see if there is any change. Did this problem start right after the engine was rebuilt? If so then probable cause is a wire was damaged while installing motor. Bad headlight relay?

From Loren:

I repaired a short in my alternator gauge last June and discovered what may be a common problem with the alternator gauges in our cars that could result in symptoms similar to what you experienced.

I am not an electrical engineer so I'll try to explain this without stubbing my toe on any of the physics involved.

The alternator gauge in my '64 consists of a plastic gauge tray, an "L" shaped brass plate with a pivot post mounted at the back center of the gauge and two brass studs pressed through the back where wires from the charging circuit connect to the gauge and a magnet and needle on the pivot post that swing one way or the other in response to the current flowing through the plate under or behind the needle.

I found that the posts (brass studs) at the back of the alternator gauge can become loose where they pass through the back of the brass. The resulting short can cause faulty / highly variable readings due to the shorting current flow through the brass plate in the gauge.

The brass studs have small splines, similar to the teeth on a gear, that bind into the brass plate when the studs were pressed through the plate when the alternator gauges were manufactured. Over time, the studs become loose resulting in a short that also produces heat.

When the short becomes severe, your car will die at idle because not enough current flows through the gauge to keep it running. I got towed home one night when this happened to me and had to repair my melted alternator gauge when my son (a Certified Chrysler Technician) finally discovered the source of my problem.

My solution was to replace the studs pressed through the brass plate in the alternator gauge with bolts, lock washers and nuts. I also had to use a piece of printed circuit board to replace the melted back wall of the plastic gauge tray and to make centering washers to hold the gauge in the proper position on the circuit board in the dash.

The brass plate was originally held to the plastic tray by nuts fastened to the studs pressed through the brass plate. I had to fasten the brass plate to the gauge tray with small nuts and bolts drilled through the bottom of the gauge tray because the short melted the back out of my gauge tray.

From Mark:

On my '63, this was caused by high resistance in the charging circuit. I cleaned up the header connector and got it to improve. Another suggestion by others on the list got rid of the rest of the movement.

I went to an Auto Zone and got a Wells, # VR706 voltage regulator. It's not correct in appearance. But, it's electronic & is a direct replacement for the old mechanical regulator. Problem solved!

Question from Don (1963):

I have a 63 LeBaron and the gauges all went dead. The service manual says to check the voltage limiter. How do I check it? I went to NAPA and ordered a voltage limiter but it was good for 64 and up. Can I use this one on a 63? 

Reply from Dick:

Probably it is electrically identical, but you may have to experiment to find a mounting location if it is physically different. The connections are always: 1 wire from the ignition switch that is hot when the key is on, 1 wire to physical ground on the dash cluster somewhere (which may be provided by a mounting screw) and 1 wire to provide power to the dash indicators. Before you go to that trouble, find the wire from the ignition switch as described above (your FSM will tell you what color it is) and make sure it has 12 volts on it with the key on. If it doesn't, you may have only a blown, dirty, or loose fuse, or you may have a bad switch (but I doubt that, since none of your accessories would work either). Your voltage limiter is probably mounted within the temp gauge indicator on the dash, that was a favorite trick of Mother Mopar in the 60's, although I don't have any specific info on a 63. If you do find 12 volts going to the gauge regulator (AKA voltage limiter), then check the wire to the temp sender at the engine block to see if you have a pulsating 12 volts out there with the key on. If you do, there is nothing wrong with the voltage limiter, and your problem is more likely a poor ground at the gauge cluster mounting. Check all the screws for bright, clean surfaces. 

Question from Alison (1963):

For some reason, my oil pressure gauge began to climb suddenly.  It is always in the normal range, but now it was climbing above that. I stopped and could find nothing wrong (my fluid levels were fine). Gave the car about a half hour rest then decided we'd try and make it the rest of the way home. For the remainder of the drive if I tried to go over 45-50 MPH my oil pressure would immediately rise above the normal "zone". Can anyone give me any ideas what this might be?


From John:

This is a common problem on the 60-63's There is a voltage limiter in the fuel gauge that starts to go bad and the gauge all except the alternator gauge will read higher then the prevailing conditions. On my first 63, had this problem and they wired an external limiter. I believe the one in the gauge can be repaired. J C Restorations does this kind of work on these gauges and I believe there info is on the club list.

From Peter:

May I suggest that you temporarily install a set of mechanical gauges under the dash. Many discount auto parts stores sell a gauge trio that includes coolant temp, oil pressure, and voltmeter. I would get the kind that has the metal sensing bulb and capillary tube for the coolant temp; skinny nylon tube for the oil pressure. Remove the existing oil pressure sender and install a 3/8" pipe nipple and tee into the block. Then install your sender into one side of the tee and the oil pressure gauge tubing into the other. Look for a threaded opening in the water pump housing for the coolant temp sender. I've noticed that many big blocks have an opening on the RH side (facing the engine while standing in front of the car) that was sometimes used for a "COLD ENGINE" lamp. (My 65 New Yorker had this light.) Anyway, my whole point is that you should figure out whether you really have an oil pressure problem. I'm not familiar with early 60s Mopars, but I know that by mid 60s Chrysler was using a small voltage regulator mounted behind the dash to power the gauges. Sounds to me like you may be having problems with that component and it would be a shame if you started doing unnecessary engine work.

Follow-up from John:

While this would work, I wouldn't recommend it if for no other reason than they would look plain awful in a car such as an Imperial.  I've seen stuff like this at car shows & some of the comments stuff like this draws on cars that these look way out of place on.  Would go something like "gee, it looks like he replaced every nut & bolt on the car, why couldn't he spend a couple bucks more & fix his gauges". Also gauges that low certainly don't encourage safe driving habits and once you put something like that in & it works, you probably will never find the time to fix it right. Since this is an easy fix, I would do it correctly or live with it the way it is.

From Mikey:

For the peace of mind - since sometimes we don't see the needle is at zero, or max , for some time - install a "Murphy" switch! From the name " Murphy's law", and for brevity I won't get into the mechanics of the installation, but basically if the oil PSI drops too far or it gets too high, it interrupts the coil and the engine quits before it gets very expensive to fix! We have had them on all sorts of industrial and heavy equipment for years and years, the stuff that costs super big bucks to rebuild if it runs out of oil PSI. Or gets so hot something breaks. 

From Mark:

My '63 used to do a weird thing. When the ignition was off, the gauge would rest at the lowest point, just like it's supposed to. But, whenever the ignition was on, before the engine was started, the oil-pressure gauge used to peg out at the maximum. Once the car was running, it would back down to normal. I figured that for some strange reason, this gauge was working in the opposite way it should. So, high reading = low pressure, low reading = high pressure. There were a couple of times while on the road that the gauge would rise up. I soon learned that meant I needed to add a couple of quarts to the crankcase. If your gauge stays down when the ignition is on and the engine isn't running, then ignore this post. If, like mine, it sails off to the top of the gauge, then your gauge may be weird like mine was, and you're experiencing a low oil pressure condition at higher speeds. One thing that might be a good idea is to change your oil and filter. If this car hasn't seen much sustained, high speed driving, some goo inside the engine may have loosened up and is now clogging the filter or internal oil passages. Especially if there was a bit of heat added to the mix, such as when the car overheated.

Question from David (1963):

I have been told that you should not ground the sender wire to see if the gauge works. Is this correct or not and if so how does one check these gauges? I put in a "new" sender unit which briefly gave a 3/4 reading before slowly dying as did the previous gauge?

Reply from Dick:

The electroluminescent system operates the illumination of the display of information on the gauges, not the innards of the dash gauges themselves.

The testing methods are not affected by the type of display illumination, and our previous statements are still in effect. Grounding the tank or other sending unit wires for a few seconds will not hurt anything -just don't leave it grounded with the key on for more than a few seconds. This is to see if the display unit goes to full scale - if it does, your gauge unit and regulator are fine. If it doesn't, you know where to look for the cause (behind the dash instruments).

If you make contact with the 250 volt AC terminals while poking about behind the dash units, you are likely to regret it!

Question from Brad (1963):

I own a '63 Imperial and during the first year, my oil pressure and temperature gauge needles would stabilize in certain, familiar places as expected. After warming up, the oil pressure needle would be positioned towards the high side, approximately three-quarters of the full travel.  The same with the temperature gauge. In my experience of driving this vintage, this is normal gauge operation for Chrysler cars.  However, these gauges simultaneously changed. The oil pressure and temperature gauges still work, receiving the information from the senders but both gauge needles now position themselves (after warming up) towards the low side, approximately one-quarter of the full travel of the gauge.  Has  anyone experienced this and has diagnosed a fix?  

Here is what I have checked so far. Initially, I disconnected the pres sender connection, no change in the temp gauge. Next, (restored pres sender) disconnected the temp sender, no change in the pres gauge.  Next, changed the temp sender, n/c in either gauge. Next, measured supply voltage to temp gauge, approximately 12 volts, normal. Disconnected supply to the  fuel gauge (power daisy-chained from temperature to fuel to pressure gauges), n/c. Reconnected fuel gauge, disconnected supply to pres gauge,  n/c in temp reading. Does it sound like my gauges are bad? Funny they would both go bad at the same time. They still read but at a lower position. I am certain that actual temperature and pressure has not changed.  


From Jeff:

Sounds like a constant voltage regulator problem. These are used for the instruments (not the same as your main electrical system's regulator), and they provide stability to the gauges so they are not moving all the time. You might want to check the inputs and outputs of that before replacing it.  

From Dick:

You should not have solid 12 volts at your gauge units. You should see the output of the gauge regulator which is incorporated in the first unit on the "Daisy Chain" you mention, and it averages 5 volts. It actually pulsates between 12 and ground, at a duty cycles such as to produce the 5 volts that the gauges operate on. If you do indeed have solid 12 volts, as you mentioned, you probably have some damage to the dash units from overheating. Verify if this is the case (the solid 12 volts) and if it is, disconnect the 12 volt supply to the dash units until you locate a replacement gauge regulator, before any more damage is done. If, on the other hand, you DO find the pulsating 12 volts, relax, your problem is most likely a poor ground to the metal frame which all gauges are in contact with, that is the return path for the indicators. Just tighten some screws that look to connect the gauge panel to the car body, or even add a ground wire under a mounting screw of one of the gauges, and connect the other end to something really grounded, like the body, or something connected to it. From your description of the symptoms, I would bet this latter problem is the more likely, but don't ignore the first paragraph above, on pain of ruining your dash units!

Follow-up from Brad:

Is it true that a solid 12 volts from the fuse box is applied to several points, ashtray light, blinkers, etc.., and to the temp gauge. From the temp gauge, power distributes to the other gauges.  I have heard of a gauge regulator.  Does anybody know where this device is mounted?

Reply from Dick:

One of the three gauges receives a supply of solid 12 volts, then regulates it down to 5 volts with the pulsating gauge regulator, and distributes the "5" volts to the other two gauges. I think in your year car, the regulator is incorporated in the Temp gauge, so you would see three wires on that gauge, and only two on the other two gauges. If this is the case, the regulator is hidden inside the temp gauge. If you have seen the pulsating voltage, it appears your regulator is OK, and I'm back to suspecting the ground to the gauges. In the interest of historical accuracy, this system (the pulsating "5" volt gauge regulator) is common to many cars, probably a majority of cars from the 40's through the 70's, since so many used the "King Seeley" gauges. Most brands use a separate little bathtub shaped box for the regulator, only Mopar, to my knowledge, incorporates it in one of the dash units. I wish they didn't, it would be easier to service when it fails (which is quite rare, actually).

Follow-up from Rolland:

I also have a 62 300 and if I am not mistaken the temperature gage also contains the voltage regulator for the temperature gage and also the other gages. This is not what you normally think of as a voltage regulator. It provides a pulsating voltage which I believe is designed to average 5 volts. I think it is accomplished by a bi- metal bar similar to the actuator for the gage readout.

Reply from Dick:

You're right on Rolland. The pulsating source is called a regulator in the service literature, though, so I also use the term.

Follow-up from Brad:

I found the Voltage Regulator built into the Temperature Gauge (which supplies voltage to all except the Alternator gauge) was beginning to fail. I bypassed it and installed a discrete Voltage Regulator (from a '67) and all gauges began working including the Gas Gauge! It was a nice surprise . . . and the regulators are still available at NAPA.

Question from Norm (1964):

My '64 runs out of gas with a 1/4 plus on the gas gauge.  Has anyone else had this problem, and is the fix in the tank or the  gauge?


From PEN:

Is the gas tank dented in from either a plugged gas cap, or someone trying to, at some earlier time, back up into a foot and a half of snow? Many are...

Follow-up from Norm:

The tank is not dented. I was talking to the previous owner and was told that a new sending unit was installed before the car was parked 12 years ago. I have come to find out from him that they were "a bunch of buffoons". The story he told me of the shop and there attitude has me surprised that it does not run out at 3/4. The car was his dad's before his dad passed away and he had forgotten about the gas gauge problem. With this new info. I should have no problem getting it fixed. The sender has only about 1 year use, and 12 years storage.

From Norman:

If your gauge is ok and your sender is too optimistic, bend the arm UP so as to dampen its enthusiasm.

Follow-up from Norm:

Last weekend I finally tackled one of the last repair items on my recently acquired 66 convert, the gas gauge. Turns out it was the sending unit in the tank. This fact was easily determined by detaching and grounding the feed wire to the sender and observing a "full" reading on the gauge. I went to my local Dodge dealer and ordered the gasket and filter for the sender and applied them to a sender I had plucked out of a 65 parts car. It now works just fine- so does the Sentry Signal with the new bulb I installed.. Interesting note: when I tested the sender using my 64 as a mule, it registered high under all conditions . I just found out why this is. The 65/ 66 models which are equipped with "Sentry Signal" send a slightly reduced voltage to the sender thru the relay and , I guess, the potentiometer ( did I get that right, Dick ? ) that is attached to the float arm is calibrated to operate at a reduced voltage when compared to a 64 and older. Moral: Do not use a 65/66 sender in a 64 or earlier Imp, unless you are an incurable optimist, or want to be perpetually "high". Also noted, the problem with the original sender in the 66 was a fuel logged float. Someone told me that Ford sells a float that will fit perfectly. I'll let you know . Finally, this is a VERY EASY REPAIR. Just put the car on a lift and disconnect the battery first. NO NEED TO DROP THE TANK, there' plenty of room to back the sender out of the tank.

Question from Johan (1965):

My fuel gauge reads full 24/7 with the key on, accept on occasion and only when I fill the tank up, it drops to about 1/4 perhaps less, then back to full as I pull out of the station on to the street.

I just up'ed the amps with a new alternator to 65 just before it started.  If the sender is shot then could it read full instead of empty?  Is it the float? Where is the float?  

Reply from John:

This sounds like the float. I've had this problem on several of my cars. On a 63 Imp, it would go to full with just a few gallons of gas & never go to empty. I've had a couple of others that the needle keeps moving all over the gauge. This item is a bit costly to replace these days. I've seen adds in Hemmings on rebuilding these. I've also seen a friend take a couple of these & clean the contacts & replace the float if it was leaking & they worked well.

Question from Mark (1965):

I have a '65 Crown Four-Door, and I am experiencing problems with a defective alternator gauge. Periodically and without warning, the ignition system cuts out completely. This sometimes occurs when attempting to start the car and has happened while I'm driving. I know that the alternator gauge has been getting hot because the plastic is melted around one terminal.

While I am trying to find a new gauge (does anybody have one?), can anyone suggest a workaround solution. Would it be possible to bypass the gauge, using a circuit breaker in its place? If so, what amperage would I need to use?

Or does anyone have any other suggestions?


From Dick:

You don't need to use a circuit breaker. Just connect the two large wires to the one healthy post. The gauge will no longer register, but your car will work just fine that way, and the gauge will not get hot, as there will be no current going through it.

From Hutch:

Do not put a breaker or fuse in place of the amp meter. If necessary, just jump it out with a wire of equell or larger than the wires coming/going to it.

Question from Cory (1965):

I finally got my gas gauge working on my Imperial. So now all my gauges work except the ammeter gauge. I've looked in my bible (FSM) but it really doesn't touch on the subject of diagnosing the problem. The ammeter doesn't work at all (no movement ever). Any ideas?

Reply from Dick:

The most likely possibility is that the dash unit is broken internally. This is not a common failure, so before you go to the expense of replacing it, make sure that the connections to the dash unit are correct, tight and clean. There should be two large wires, one on either screw post connected to the gauge, in addition to other wires of more common size. If perchance the two large wires are connected to the same post, the gauge may have failed and someone thus bypassed it so the car would still operate. If you move one of the large wires to the other post, and the gauge is bad, the car will be essentially dead (no juice). If you do this, and that is the result, start looking for a new gauge. It is OK to use the car the way it is, you aren't hurting anything. There is another possibility: That the shunt (only) may have failed, making the ammeter super sensitive, banging from one side to the other, and causing the previous owner to bypass it as discussed above. So, if you reconnect it properly and you are confronted with the overactive gauge syndrome, your shunt has failed. You can easily repair this by fabricating a 14 inch long #14 wire with solder lugs on each end, and connect this between the two posts on the gauge unit. This wire will get somewhat warm in operation, so don't bunch it up or tape it in a lump, just let it drape around back there so it will be cooled by the breezes. By the way, if you get through all this, and every thing looks kosher now except the gauge reads backwards, reverse the connections to the two posts on the gauge. Needless to say, disconnect the battery before fiddling with these wires, that area is always "hot", regardless of the key position.

Question from John (1965):

Well, yesterday I drove up from Tucson to Picacho Peak and back (about 90 miles) in my '65 to see how it behaved on a hot day. The temp gauge was in the low 90s. I stayed at or below 75 the whole way. Anyway, after awhile my cheap Pep Boys mechanical gauge was reading 230/235, which in the old days would have had me very concerned. Well, still does. But the factory gauge works, too, thanks to a new sending unit. It stayed just past the center of its sweep, about like so: 

C                                    -----------------I-------------          H 

That doesn't seem hot to me, and the motor didn't seem overheated when I stopped for a soda. It did send a couple of quarts of coolant into my overflow tank, though. (this morning the overflow tank is still full, but so is the radiator.) All this with no air conditioning, too. When/if I get that fixed, won't it add another 10 degrees or so to the temperature? As a point of reference, when the mech. gauge reads 180/190, the factory gauge reads at the left end of the "normal operating" line (those with '64-66s will recognize my crude art I hope). Which gauge would you believe? Someone once told me that the mechanical gauges tend to read hot because they pick up heat from the block, unlike electric gauges. I'd like to get rid of this gauge so I can put back the sender for the "sentry signal" but obviously I'm too nervous.

Reply from Michael:

My 68 has a similar gauge, and also reads very near the low mark of the normal range when I use a 195 thermostat (I do now), or on the low mark of the normal range with a 180. This roughly matches your comparison of the mechanical and dash gauge. Mine has a very effective cooling system, and when the AC was working, it didn't affect the temp at all, except idling in traffic, and then very little. I was in Florida where humidity is hard on "Yankees", very good for radiators. I would guess the best system would be stressed where there is almost no humidity. One point you mentioned that I want to address. Your overflow tank stayed full when cool. You may know, but if not, maybe I can keep you from learning like I did - you have to have a radiator cap designed for use with an overflow tank. The first time I put a tank on a car not so equipped, I did not change the cap, and all I did was manage to move the coolant one way, out of the radiator. Better to tell you something you already know than not mention something you need to know.

Question from Jan (1965):

I need some help. No instrument is working in the dash panel (Ammeter, fuel gauge, temperature gauge and oil gauge). What is wrong?

Reply from Dick:

Are you sure that the ammeter isn't working?

That is a completely separate system, not related to the other three gauges other than the fact that all power flows through it. Verify that all 4 gauges are not working, please, before we go off on a wild goose chase. If that is indeed the problem, my first question is: what else isn't working? Does the engine run, and do the headlights light?

If the ammeter IS working, and the other three are dead, that is relatively easy to understand. Most likely the ground to the instrument cluster has failed. Another possibility is that the ignition switch feed to the gauge regulator is disconnected. However, neither of those problems would affect the ammeter.

Follow-up question from Jan:

Yes the ammeter isn't working. I know the ammeter is a completely separate system.   I have the FSM, but in the wiring diagrams, I can't find any voltage limiter.

Reply from Dick:

The voltage limiter has another name. In some books it is called the "gauge regulator". It is inside the temperature gauge on most mid-60's Chrysler built cars.

Take the following steps.

1. If you look at the wiring diagram, you will see a wire from the ignition switch circuit that has 12 volts if and only if the key is on. Follow that wire to the temperature gauge terminal which has the same wire name on it. This is the power supply to the voltage limiter inside the gauge. Make sure that there is 12 volts there when the key is on. Also make sure that the metal case of the gauge units is securely grounded (earthed) to the frame of the car, with bright metal contact at the attachment points so there is no question that the ground is good.

2. Now notice the wire from the temperature gauge that connects to the fuel gauge and to the oil pressure gauge. There is only one wire that does this. This wire is the output from the voltage limiter. If you put your meter on that wire with the key on, you should see the meter vibrate slowly between 12 volts and ground, about once per second. If this is happening, your voltage limiter is working OK.

3. Now notice the other wires, one from each of the 3 gauges. One goes to each sender unit. The oil pressure gauge wire goes to the bulkhead connector and then to the oil pressure sender on the rear of the engine. The other gauge wires go to the fuel tank sender unit and to the temperature sender unit, as you might guess.

If all of the above things are right, your gauges should be working now.

Your ammeter problem is separate. You will have to look at the terminals on the ammeter gauge to see if it is connected. If it is connected, there will be two large wires, one to each post on the back of the gauge. If both wires are on the SAME post, the gauge has been disabled, probably because the shunt has failed. If it is connected the way the wiring diagram shows, and it does not work, the gauge unit must have failed internally.

Correction from Bill:

The voltage limiter is in the fuel gauge NOT the temp gauge.  I'm re-doing the dash cluster of my 1965 LeBaron, I have 5 gauges of each dash gauge & all fuel gauges have the "limiter" & none of the temp gauges have the "limiter". 

Question from Jan (1965):

I  now have a working gauge regulator which fixed my oil and temperature gauges, but not the fuel gauge and I still have 12 volts in the dash when my ignition is off. Any ideas on how to repair this problem?

Reply from Steve:

Start by momentarily grounding the wire at the sending unit. The gauge should go up past full. Don't leave it that way more than a few seconds as gauge damage could result. If the gauge does not go up to or past full then you know the problem is from that wire forward. Could be the wire itself, the gauge, or power to the gauge. If the gauge does go up to or past full then you have a problem with the sending unit. Make sure the sending unit/tank have a good ground. The sending unit could be bad or it could have been installed incorrectly allowing the float to hang or the float could have sunk. It sounds to me like your sending unit was either the wrong one or not installed correctly. Not to be offensive, but if this one stumped your mechanic I would start looking for a new mechanic before you need a major repair.

Question (1965):

The gas tank sending unit was replaced on my car but the gas gauge still doesn't work? Any other common problems before I get into the complicated stuff?  I tested voltage at the sending unit and it was a pulse this correct?

Reply from Dick:

Yep, that's what you should see. Your electrical system and dash unit is probably OK. If you're sure you put in a good gauge sender (you checked it with an ohmmeter?), then your problem has got to be connections. Either the tank is not grounded to the frame (most likely) or the wire connection to the sending unit is flaky. I assume you verified that the float floats? What kind of no workee do you see. Allatime nuttin? Allatime full? Random readings. Whut, hey?

Follow-up question from Jim:

It reads intermittently high or low. Where is the ground strap you mentioned mounted? Am I correct in remembering that the sending unit can be removed with the tank in the car? Are sending units available?

Reply from Dick:

I didn't mention the ground strap because I do not know where (or if) it is. But you don't need one, so long as your tank mounting hardware is clean, unpainted, and tight. Just verify that you read no more than a few tenths of an ohm from the tank itself (best to check this right at the mounting ring for the sender) to the car's frame. If you see some resistance there, clean the straps, bolts and other hardware to get a good ground. A poor ground will always make the tank read too low. If this is not your symptom, then grounding is not your problem. If it is erratic and sometimes reads too high, you either have a problem with the sender or the dash unit, or possibly the interconnecting wire, but there is nothing the wire can do to make it read too high either, except possibly short to ground, in which case the gauge would peg above full and stay there as long as it was touching ground, (and probably burn out the dash unit).

The sending unit should still be OK if you can clean off the gook without damaging the rheostat wires inside the little housing. If you see around 10 OHMS full and 60 OHM empty, and the float is not full of crud, it should be fine.

Question from John (1965):

My gas, amp, and temp gauges don't work....Is there any connection between these gauges...????

Reply from Dick:

The gas, temp and probably the oil pressure gauge all require the gauge regulator (also known as the "voltage limiter") to operate. The AMP gauge is totally independent of those other units, so you must have two separate problems if your symptom is as stated. Further, if your oil pressure gauge does work, then your gauge regulator must be OK. If the oil pressure gauge does work and it is electrical (connected with wires rather than a steel or copper tube), then you have a very strange situation with your temp and gas gauge.  

Question from Rob (1966):

My oil pressure gage is slow to come up to its normal position.  Prior to having my oil changed last week, the needle would immediately > and steadily move from the left to near extreme right when I start the  engine. This has been so for the 2 yrs I have driven the car. It is my daily driver. Now the needle 'sluggishly' comes to lower side of half way and the slowly moves to the position I have observed as normal when I start the car. The performance is similar to extreme cold engine starts (-30C).  The first thing that comes to mind is defective filter. The place I had my oil changed recently changed brand names (to Fram, I think), has anyone had or heard of a defective filter? The second thing is too heavy an oil for the temp, but this seems unlikely as the temp is still just above freezing ... hardly enough to 'thicken' oil ... and the oil is supplied from a 500 gal drum stored inside. The sending unit? Weak oil pump?

Reply from Dick:

If your car has an electrical gauge, the indicator should move up the dial in slow, pulsating surges, perhaps 1/4 of the way to its steady state position with each surge, which should occur about once per second. This is the gauge regulator doing its job, and is normal. If it used to fly up scale immediately, it is either not an electrical gauge and you had very thin oil, or there was something wrong. A slow reaction is pretty normal, even for the other type of gauge, which I call "mechanical", even though it is more properly called hydraulic, I guess. In any case, see if your gauge sender has a wire on it. If so it is electrical. If it has a tiny tubing on it, it is mechanical. Others on the list with a 66 will probably jump in here with the answer to this. Not knowing what part of the country you are in, I cannot comment on the oil you are using, but consult your owner's manual, don't trust the guys in the Quickee-Lube places. If the oil pressure is actually in the normal range when the car is thoroughly warmed up, there is nothing wrong with your oil pump, or anything else mechanically. I cannot fathom why a Fram or other name brand filter would be causing this problem, but I suppose if it is draining dry between starts, it could cause a slow rise of oil pressure. It would be wise to change the filter again, just to eliminate it as a cause. They only cost a few bucks, and you might save yourself a lot of unnecessary wear on startup if you got the one in a million that has a bad check valve.

Question from Wayne (1966):

I am having trouble with the ammeter gauge on my '66 Imperial. The plastic gauge housing is melting! The meter leads and the wire leads are corrosion free and the connections nice and tight. My alternator is a later model replacement that has a higher output than the original 1966 model. Is this the cause of my trouble?


From Dick:

Probably. Your car came with an alternator that was adequate for the accessories fitted to the car. This is typical of the kind of problems one can get into by "upgrading". If you put a 100 AMP alternator on a car that is designed for a 45 AMP alternator, something is going to get fried!

From Carl:

The higher available output of an aftermarket alternator won't come into play unless you have something that needs a LOT of current. Say for instance that your car requires 40amps at 13volts to run headlights, heater and ignition. Your 50amp alternator has no problem. If you swap that for a 100amp alternator, the car will still only pull 40amps with headlights, heater & ignition. The difference is when you get a high current load. For instance, you left the lights on and the battery is dead, now the alternator needs to provide 40amps to run your regular stuff, AND more to charge the battery. Say the battery needs 20 amps, now you are up to 60 amps which is easy for the alternator but if your amp gauge and associated wiring only handles a max of 50, you're in trouble. Ideally only the fusible link should burn, but you never know.

I don't know enough of the insides of the gauge to tell if there's something there that can be cleaned, but if you get heat, there is resistance somewhere.

From Gene:

I had the same problem with my '65. The connections appeared to be tight, but when I removed the gage to replace it I found that the connection in the gage itself where it connects to the stud was slightly loose. Enough to raise the resistance. I checked the connections on the replacement gage for tightness and I have had no problems for the last five years. The old gage could be used again with a little work where the melting took place.

Question from Brad (1966):

While I was fixing my vibration problem I also wired up the fuel tank sending unit. I ordered a ground strap from Year One and installed it on the unit outlet and attached it to the frame grounded fuel line. I don't have a multi-meter but I do have a test light. I checked the wire at the tank for current. I got a light with the key ON and OFF. It was kind of weird. It "pulsed" dim to bright. My thought was that this wire was in the same circuit as the clock, could it be? It pulsed like the winding mechanism of a clock would as the contacts close and open. I have another sending unit so I wired it into its own circuit using the tank wire for power and grounding it to the frame with the test light. As I moved the float back and forth, the pulsing light got brighter and dimmer. I guess that only proved that that sending unit works. I checked the gas gauge with the float at both the up and down positions. The gauge didn't move in either state. I didn't pull the unit in the tank out. I don't own a brass drift and didn't want to chance causing a spark (the seal leaks a little. I got a new seal too so I'll do it all at one time). My questions: Is the tank wire supposed to have power to it at all times? Is it in the same circuit as the clock? I seem to have lost time during all this. I there any danger in leaving this wire attached to the sending unit if the wire is NOT supposed to have power to it at all times?

Reply from Dick:

The pulsating light means your gauge regulator is working correctly. The last time we talked, this was the wire that had been grounded, right? As I said at that time, grounding the wire TEMPORARILY should take your gas gauge to a full indication. If it does not, the problem is with the indicator or the connections to it, regardless of any other situation at the rear of the car. Leave the tank sender alone until you figure out the following situation. Your sender may be just fine. 

Turn the key on (at least if your car were normal you'd have to get power to the circuit), then take your test probe and verify that you see the pulsating signal on the "S" terminal on the fuel indicator, and a solid ground on the metal of the indicator unit.

The way to verify a solid ground on anything is to connect your test probe "grounding" alligator clip to something you know has solid 12 volts on it, like the main body feed from the battery, and probe with the sharp point on anything metal to verify that you have a good connection, the light will light (yes, the polarity is reversed, but bulbs don't care), then probe your gas indicator or mounting point to verify a good ground. 

90% of the time, this will locate your problem, but if the wires are all connected right and the indicator still doesn't respond to grounding the "S" terminal, the indicator is indeed burned out, (which I suspected way back when this all started and you said the wire was permanently grounded at the rear). One can get away with grounding the sender's wire for a few seconds to verify that the dash indicator is responding, but it will overheat and burn up if the wire is left grounded for more than a few seconds. 

The fact that the power is there all the time is a separate but definite problem. It means your accessory circuit is on all the time, and if you leave it that way, it will be running your battery down slowly, and could also cause other problems. Please consult your FSM and the IML archives to see how this circuit works and is supposed to be connected. (The gauge sender wire comes from the gauge regulator AKA voltage limiter, that's the dingus that does the "pulsing") and the archives are jam-full of posts about it, some quite recent. 

You are going to have to get at the connections at the gauge cluster. I suspect the car is mis-wired at the fuse panel, with the "I" wire to the regulator connected at the wrong terminal on the fuse block, but you are going to need to carefully follow the colors and connections as laid out for you in the FSM to dope this all out. It could indeed be connected to the clock power source, but it shouldn't be! If you don't have an FSM, you are going to have to get one to troubleshoot this problem. Are we talking about the 72 or the 66 here? I'm assuming the 72 in all the above, but since I am not personally familiar with either of them, I'll have to trust your eyes to tell me what you see under there. As a temporary expedient, you could just lift the black wire off the gauge regulator/voltage regulator terminal, that should stop the constant current drain. Be sure to tape it up, it is hot all the time (and shouldn't be, it should only be hot when the key is on!). 

It ain't rocket science! (I know, I've done both!). Just disconnect the battery and slither under there with a good light and a comfortable pillow. Take your shoes off so you don't soil the headliner!

Question from Gary (1966):

I have a 66 Imperial, and my gauges like the oil pressure, temp. and the fuel seem to be acting funny.. What happens is when I start the car they all go where they are suppose to be, then as if they loose there power they head back to the left, for a few sec. then back to where they were, and they do this all together. Sometimes they stay up for a while, then they head back down, then come up again...


From Dick:

This sounds like a loose wire or ground on your gauge regulator. I'm not certain which of the gauges incorporates the regulator on a 66, but if you can slither under there and find the only gauge with 3 wire connection posts, that's your gauge regulator location. Check all three wires for a sturdy connection, and also make sure that particular gauge is well fastened to the panel, as the mounting screws provide the ground path for the regulator. Also make sure the gauge panel itself is well tightened to its mounting surface. Maybe someone with a 66 FSM can look up and tell you which gauge unit incorporates the regulator. There's a remote possibility that the problem is in your ignition switch, but if that were the case, other accessories that go on and off with the key would be acting the same way (intermittent, that is.).

From Bob:

Page 8-51: "On Imperial models the voltage limiter is contained inside the fuel gauge".

From Mark:

Dashboard Voltage Regulator. Don't know if your cluster is mounted to a circuit board or if you still have separate gauges. If they're on a circuit board, the regulator will be mounted on it. It's silver, about an inch long by 1/4 inch wide and will unplug. In my '63, it's mounted in the fuel gauge, non-removable. Got to replace the gauge. My '68 is as described above. Not sure when the change happened.

From Al:

At Dick Benjamin's suggestion I looked in my '66 Imperial (I love that word) shop manual. My '66 gauges do something funny altogether too although it's been so long since I paid attention to it I can't quite remember what. Anyhow here's what I found. First off, the voltage limiter on Imperials is contained in the fuel gauge. Under Service Diagnosis Your precise condition is not listed but the following is: ALL GAUGES READ HIGH ("against the peg") AFTER IGNITION IS TURNED "ON" Possible Cause: a) Faulty voltage limiter (stuck points or an open heater coil). b) Cluster not properly grounded to panel. Correction: a) Test voltage limiter. b) Tighten cluster mounting screws. And: To quickly test the voltage limiter in the vehicle, connect one lead of a voltmeter or test light to the temperature sending unit and the other lead to a good ground. Leave the sending unit lead wire attached to the sending unit. Turn the ignition switch to the "ON" position. A fluctuating voltmeter or a flashing light indicates the voltage limiter is operating.

Question from Carl (1967):

The Amps gauge needle on my car never stands still. It's a 383 engine with virtually nothing on it that should cause this shaking of the needle. No air conditioning, no power seats, no power windows, no pollution control stuff, just plain normal items like a radio. When I first start the car the needle flies to the far right so hard you'd expect the dash to shake. Then after about a minute or two it starts to drop to the slightly above middle position but shaking all the way. On engine idle, the needle shakes from about a little below middle to about almost the first marker above middle. It has done this for a few years now. I changed the gauge one and that was a job not to be attempted by me to many times. I've put in a new battery, changed alternators three times, changed positive and negative battery cables, checked and cleaned any ground connections I could find. The one thing that really bothers me is that the replaced gauge could be just as messed up as the one I took out. Anyone out there have a new one they want to sell? Or anyone have a possible solution to the nervous Amp gauge needle. I know it is not supposed to be this way cause I've had the car since 69 and it is something that just one day started. A friend of mine once told me that the cars power is involved with this gauge and if the gauge goes out, the car stops and no can restart till gauge is replace or jumpered. Anyone know if that is true also?


From Mark:

The gauge on my '68 Imperial does much the same thing, though maybe not as radically. It "vibrates" around the center. Usually, this stops after awhile. I have always assumed "that's just the way it is," since the car always starts and, until recently, has had no problems.

Follow-up from Carl:

Don't really think the amp gauge needle is supposed to wobble, shake or whatever. On my 67 Imperial it is solid in one place once the car is running for a few minutes. Had a 62 Newport and a few friends of mine with Chrysler products and all amp gauge needles are steady. Only thing that bothers me is that one person that is supposed to be a mechanic said that if the amp gauge goes out, you car is dead. I wonder if that's true. That shaky needle has bothered me for a few years now. Tried a new gauge once and changed alternators twice. Checked all known ground connections, replaced volt regs a few times and the amp needle still shakes. Anyone else got this problem or know the answer to why?

From Joe:

On cars equipped with ammeters, and most Imperials I know of are, the car will indeed go "dead" if the ammeter circuit opens up.  Wobbling or erratic pointers on ammeters usually indicate either a problem with the voltage regulator/alternator/generator or a bad connection to the ammeter.  If anyone has been working under the dash and disconnected gauges at any time suspect a loose connection.  The ammeter passes all current to lights, accessories and ignition circuits in the car.  Another point of bad connections is a bulkhead connector on models which have such a connector at the firewall.  Bad grounds to major items like the engine block to firewall (body) etc. can also cause erratic meter operation.

From John:

I've not attacked this on a car, but the basics of the circuitry are universal, so here goes my thinking: 

1. Decide if the current is really pulsing, or if the gauge is overreacting. Get a clamp-on ammeter (if you like nice tools) or an in-line ammeter (you may have one already) and put it on/in the circuit leading to the ammeter (which is a parallel to the main charging loop of alternator and battery - there's a high-ohm resistor in there that limits the current through the ammeter shunt to a tiny but proportional part of the main loop current). If that ammeter dances, then I suspect a bad field winding in the alternator (rebuilds often have this, because the units work well enough and many older cars don't have ammeters). 

2. Assuming, though, that the real current is fairly steady (or that you would just like to solve the appearance of the problem, not exorcise the entire demon completely), then you need to increase the inductance of the ammeter shunt circuit. This is the electrical equivalent of adding road-hugging mass, so that every little bump doesn't disturb the ride (in this case, needle position). Kind of seems like an Imperial sort of thing to do. Anyway, there was/is probably an inductor (fancy term for multi-turn coil, usually over an iron or ferrite core) in the ammeter circuit (anyone know specifically if these cars have separate inductors or if its internal to the ammeters?). If it goes short internally, it will act like a fewer-turned coil and the ammeter will overreact (clue: you said it pegs at start up!). No matter, it will do no harm at all to add more (except for a slight scale error in the reading). I can't readily tell you how many turns are required, not knowing the value of the present resistance, etc., but if you're game for the experiment, just get some wire about 2 gages bigger than your [present ammeter leads (to minimize added resistance). Use magnet wire (varnish only, no colored plastic insulation, available at Radio Shack or through McMaster-Carr). Wind a few dozen turns tightly around an iron core (a 1/2 inch bolt, say 2 or 3 inches long will do fine, and it makes a built in mount if you have a handy hole and keep the threads uncovered). wrap the bolt first in some electrical tape to prevent rubbing of the wire and possible shorts. Then put your new coil in the line from the alternator (or battery) to (from) the alternator. You should notice a reduction in bounce, because the inductor will filter out some of the pulsing in the current (it's an AC filter). I may be guessing too low on turns count, so you may need to try again if the bounce is not reduced enough. I may have guessed too high (less likely), if you see that the reading is way less than full scale. 

From Elijah:

Try replacing your voltage regulator. This little item is the most likely cause of amp gauge wiggle. I've had this happen on two '71 Imperials, as well as a '67 Newport, and the cause was always the voltage regulator, or a bad connection at the voltage regulator. And yes, on your Newport, the amp gauge does run current for the whole car -- if the gauge isn't properly connected, the car will not start or run. When I was 16, my Mom's '67 Newport wouldn't start -- and NONE of the local "mechanics" could figure out why. Then I spent five minutes under the dash tightening the amp gauge nuts, and voila -- problem solved.

From Gene:

I am told that replacing the mechanical regulator with an electronic regulator will solve the problem. I intend to switch someday. As for the meter going bad and shutting down the car electrics; mine did go bad. The back of the gage where the power connections were made apparently got loose and over heated and melted the back of the gage. This caused an intermittent connection and when the connection is broken the engine will not start ( unless you jumper). The ammeter is not shunted and nearly all of the power used by the car goes through the gage. Check the connections on the back of the gage for tightness.

Question from Chris (1967):

As if something happened overnight, I started my car this morning to find that the FUEL GAUGE is no longer registering.............?

It was working less than 24 hours ago.

I've checked over the tank ground and the relay (sentinel system is present) but found nothing, and no reaction..... what am I missing or do I have to take apart the dash (gauge itself - sigh), or worse pull the tank (sending unit - ugh)...

Reply from Dave:

All you need to do is remove the wire from the sending unit, and ground it. Then go and turn the ignition on and watch the fuel gauge. It should go directly to FULL. If it does, then the dash unit (and the wiring between it and the tank) are OK. If it does not move, - then double-check where you "grounded" your sender wire and try again. I have found that in the vast majority of fuel gauge problems that the problem is not with the dash unit or wiring. Most of the time, - the float has developed a "leak", and has subsequently "sunk", - causing an "E" reading. Just to be sure and eliminate all the wiring though, - you may want to remove the driver's side kick panel, there is a 6-way(I think) connector here, - look for the blue wire. Ground this wire, and that will check the wiring between the connector and the fuel gauge. Not so tough to pull the tank sending unit (at least you don't have to remove the fuel tank to do it (like you do on almost all the "new" cars).

Question from Paul (1967):

Does my 1967 crown have a gauge regulator??  


From Dick:

All 12 volt cars and most 6 volt cars that I am familiar with, built prior to the mid-80's, and using analog type gauges, have a gauge regulator (unless they have computerized dash displays.) They are the same electrically on probably all cars, so you can use a universal fit type and it will work fine. On all cars it will be found somewhere within the gauge cluster, somewhere on the back of the panel or incorporated into one of the dash indicators (the only one with 3 wires on it). Most 60's Imperial hide it inside the temp indicator. I don't have a 67 FSM, but if you can't find it in yours, ask again and someone will look it up for you. I could probably find it in my 68 Manual, but I don't have it at home right now, so if you need me to, ask again and I'll look it up for you. If you are checking in your manual, follow the fuel tank sender wire back toward the dash indicator, you'll see the power feed to the sender connected to one terminal of the dash indicator (the one that DOESN'T go to the tank unit). This power feed wire comes from the gauge regulator.  They are still available from NAPA.

Question from Donald (1967):

I have a strange problem with my gas gauge, it reads 'E' with the Check Gauges light constantly on. Every once in a while the gauge wakes up and works, or at least gives some form of a reading, whether it is correct or not, who knows! Of course, the Check Gauges light goes off. FYI there are no leaks in the tank or lines, et cetera. Any Comments?? - would it be the sending unit, or possible the float in the tank?? What about the gauge or even the electrical supply to the gauge?? I haven't a clue where to start and please keep in mind that I just acquired this beautiful Arizona car two weeks ago.


From Luke:

I've just had the same problem with my '60 LeBaron. I don't know much about the electrical side of things, just that the gauge it basically a kind of resistor coil and the needle is like a power meter that shows varying volt/F-E readings according to the level of the float lever. But what I can tell you is don't be afraid to whip out that gauge and have a look-see. I took mine out last weekend in about half an hour no hick-ups at all. And it looks just as easy to put back in. That's probably the only way to really see if the float is faulty. Mine was, the earth strap that feeds current back to the gauge was snapped with metal fatigue (all the years of going up and down). This might be your problem. See what other members have to say.

From Paul:

A quick check to isolate the sending unit in the tank from the gauge is to unplug the wire on the sending unit at the front edge of the gas tank, (next to the fuel line connection), and connect the wire to the chassis of the car. Having grounded the sending unit wire, you should turn on the ignition and observe the gauge. If it swings quickly all the way to full, then turn off the ignition, your gauge is almost certain to be OK and the sending unit is corroded or damaged in some way. One time I had a failure of the float on the end of the sending unit. I simply used a float from an '80s vintage Dodge Diplomat to make the repair. If the sending unit is found to be at fault, it can be removed from the tank without removing the tank from the car. The tank should be nearly empty. If the sending unit shows evidence of corrosion, you should pull the tank and have it treated. If you have to replace the tank or sending unit, you should be able to use the tank and/or sending unit from '66 though '68 (or maybe later) full size Chrysler, Dodge, or Plymouths as well as Imperials. If your gauge does not move during this test or moves only a little, the gauge is probably at fault. Is your temperature gauge working? If it is then the voltage regulator unit is OK. If both the gas gauge and temp gauge are reading very low then it could be the voltage regulator, (a small metal unit that plugs into the back of the instrument cluster circuit board.

From Elijah:

On the two occasions that I have had problems with my gas gauge, especially problems where it worked part of the time, and went on vacation part of the time, the problem proved to be the connection at the instrument cluster. On the '71 Imperial, the gas gauge works from a single wire, which has a round connector on the end of it that attaches over a bolt that protrudes from the back of the instrument cluster. I have found that this connection suffers from two problems -- the bolt will become corroded or rusty, and the connector on the end of the wire will spread and become loose. You might want to check this connection first, as it's somewhat easier than trying to delve into the gas tank.

Question from Rob(1967):

Hey folks, I have 67 Imperial convertible. The oil pressure gauge reads about a quarter ways inside the left side of the safe operating level. I suppose this is an acceptable reading but it flirts with the edge of the low line after long runs. What kind of readings are some of you other members getting? I was considering a motor flush for a possible restricted oil screen.


From Steve:

I would first suspect the gauge is not correct or replace the sending unit before suspecting that you have engine problems. If you are guessing the oil pump pickup tube screen is clogged, most likely the most thorough way to solve this problem is to drop the oil pan and clean out the screen and the pan. <--my .02cents Motor flushes might dislodge more varnish and sludge and clog the screen even more. You did not mention if you are getting a "low" reading when hot and at idle. An oil pump story: When I first bought my '73(which has been dead for some time now) the oil pressure dropped to "zero" on it's first ride to my house. The lifters started ticking and I started to hear "low end" knocks, so I shut it off and had it towed home...knowing full well that the gauge was NOT lying. I bought an oil pump which is easy to install since it is "external". I briefly started the car up just to get it in the garage and all of the sudden it had lots of oil pressure. I replaced the pump anyway and disassembled the old one only to find worn rotors/shafts and semi-stuck pressure sleeve and spring. The problem never surfaced again with the new pump. (end story, food 4 thought) Also, I neatly installed a small, quality (Auto Meter), mechanical oil pressure gauge neatly under my recent '75 Imps dash along with other gauges(H20 temp, volts, vacuum, and trans-oil temp) The gauge reads about 65+psi when on high idle when cold...and about 25 when hot and idling in gear. '75's unfortunately don't have a factory oil pressure gauge..only a light. (thumbs down goes here) I use Castrol 10W-40.

Follow-up from Rob:

I kind of played with the wire connection on the top of the sending unit and it was kind of loose. Don't know if that could be a factor, but the readout is a little higher now. First day start idle is almost in the center of the the readout, hot idle dips down to about 25% of the readout towards the low end. Still in the acceptable range but it just seems like it should be higher. I stared running red line 20-50 a few weeks ago. Could have something to do with it also. I'll switch oil again before I do anything mechanical. On the 75 imp with the dummy light, how low does the oil pressure have to go before the light comes on? Also does anyone know the difference between a high volume oil pump a high pressure oil pump, and the standard unit? It seems self explanatory but I wasn't sure.

From Mikey:

As far as the gauge reading, they can be very misleading. I recently added a small mechanical gauge because I wasn't sure if my readings were accurate or not. On a initial start of the day, the gauge is between the center mark and the 3/4 mark, and the mechanical gauge is 50psi. After a warm up drive, the dash gauge drops to the center, and the mechanical unit reads about 35. After a really hard run and its very well warmed up, the dash gauge hardly has moved at all from where it was and the mechanical gauge is hovering around 20.  I recently changed oil and at that time had some misgivings about 10-30, but it was one weight that was suitable for all 4 cars.  

My advice would be to install a mechanical gauge, if only to verify your readings are ok, so you will at least know where your engines oil pressure is at. Whether you leave the gadget in or not is completely your preference.  The nominal setting for most oil pressure lights is 7 PSI, most of the replacement ones I sold at Napa were in that range, but you could get one for a different rating as long as the threads where it fits in to the block are the same, or you can plumb as required.  

And for standard, hi pressure and hi volume pumps: the difference between standard and hi pressure is the relief spring, the factory used a 55 PSI spring for standard.  A high volume pump moves more oil by volume than a standard one, but not necessarily at a higher pressure. The general rule of 10 PSI per 1000 rpm is usable for most engines, so standard pressures should be fine. As a final note on the pumps, the pump will move a set amount of oil per revolution of the pump, its the clearances between the shafts and bearings in the engine and the viscosity of the oil that determine the pressure. If an engine is well within its limits of bearing clearances ( main, rod, rod side and cam ) then your oil pressures should be adequate.  Usually changing from a 10-30 to a 10-40 ( for example ) won't make a huge difference.

Question from Paul (1967-68):

I can not find the location of the gauge regulator.  Can someone look up the location and a source for a new gauge regulator?


From Dick:

I looked up the gauge regulator in my 68 FSM, which should be the same as a 67. They call it a "voltage limiter", and it is incorporated within the fuel gauge dash indicator. Because it is involved with a printed circuit assembly, it is going to be difficult to replace without a lot of work by someone who is familiar with this technology including cutting runs on a circuit board. Can you tell us why you think you need to replace it? They seldom fail, usually the problem turns out to be in the wiring, either on the supply side (the "I" terminal should have +12 volts on it all the time the ignition key is on) or in the grounding of the gauge cluster to the car body. If you take a test light and probe the three terminals on the fuel gauge, you should see a pulsating voltage (the test light will blink, once a second or so) on the "A" terminal, and a solid 12 volts on the "I" terminal. If you see this, your gauge regulator is just fine, and the source of any other gauge problems you are having lie elsewhere. The "S" terminal doesn't matter for this purpose (it comes from the tank sender), but tell us what you get there also. 

Follow-up from Paul:

I can't find it anywhere in the car....HELP!

Reply from Dick:

Look on the back of the gauge cluster. You will see right behind the fuel gauge that there are 3 terminals, labeled "A", "I" and "S". These go to the gauge regulator/voltage limiter, which is INSIDE THE GAUGE INDICATOR. You can't see it, it is hidden by the back panel of the gauge cluster.

Question from Mark (1968):

It was a nice day here in NW Florida, so I took the '68 convertible out and while I was driving I noticed that the temp gauge never came up to the normal position, which is around the center of the gauge. It hovered around 1/4 of the way over from the left-- not even in the little "boxed" area on the gauge that gives you the normal range.

I drove the car long enough for it to warm up, and it's 87 degrees down here. The last time this happened on a car of mine the thermostat was bad and the car overheated. What could be causing the gauge to stay so low?


From Demetrios:

It could be the thermostat but its more likely the temperature gauge. Its worthwhile doing the test suggested to check if your thermostat is stuck wide open. If it's the gage, may be its time to install a mechanical aftermarket gage. I need to do that on my LeBaron that is doing similar tricks (i.e., temp reading is all over the place).

From Brad:

Thermostat is cheap, easy to change, and is most often the problem. Give that a go first IMO.

Question from Keith (1968):

My '68 crown has started cutting out at stop lights and sometimes while at speed. I cuts out for 1/2 second then keeps running. Only rarely does it die altogether. When this happens I've noticed that the alternator gauge goes to D. And as of this morning while at speed the gauge flutters rather quickly just below middle.  Does anyone know what the problem is? I just put a new battery in 3 days ago.  The alternator looks NEW.  I just bought the car a few months ago. 


From Jack:

Wiggle wires all over while the engine is running till it happens. You must have a wire shorting out somewhere. I would start with the small wire coming out of the distributor and work out from there. could be anything causing a dead short. It must be sensitive to bumps or vibrations.

From Don:

I once had a Fury whose spark plug-like wire that connects the coil to the center of the distributor burned in half internally. The insulation looked perfect since it was only a year or so old. It would occasionally cut out while going down the road and then start back up, presumably due to vibration causing the two burned ends to re-contact. Tough one to diagnose but very inexpensive fix. Also had a Cordoba with similar symptoms but that turned out to be a loose grounding strap between the engine block and the firewall. Either way, it sounds to me electric and not fuel.

From Jeff:

I believe your problem lies in your main lead wire that goes through the firewall. there is a plastic connector on the firewall that connects the inside of the car wiring with the engine compartment wiring. I think there is corrosion between the 2 sections and you need to unclip the harness on the firewall and get some contact cleaner at radio Shack and get rid on any corrosion on those connectors. that should take care of your problem.

From John:

This sounds like a loose or ready to break loose wire to the distributor or the ignition coil. The wire going into the distributor is very thin & it breaks off or shorts out.  

Follow-up from Keith:

Well, I had a look last night on the way home from work around 8 o'clock. Didn't quite make it home, had to stop at a gas station because the lights were getting dim! While the car was running I jiggled some wires and to my DISMAY found that the battery line on the alternator was just wrapped around and tightened down!!! No connector!!! It was all corroded and when I started to loosen the nut I noticed that the whole bolt moved. So what was happening was a grounding of the battery line to the alternator body. Also when replacing alt. with a new one I noticed that the ground wire was just wrapped around as well. This looked like a new alternator so I just assume that the guy I bought it from was a complete idiot or didn't own a tool other than a hammer!!! I'm having to get a new battery, my NEW one is no good now.

Question from Roger (1969):

The fuel gauge in my 69 Imperial does not work any tips on how to start solving this problem? What resistance should the sending unit read?


From Bill:

I have used a simple method for years to check a non working gas gauge. Simply remove the wire from the sending unit in the gas tank, and with the ignition switch in the on position touch the wire end to a good ground. Have someone watch the gauge on the dash and if when you ground the wire the gauge indicates up to full, your dash gauge is probably OK. If when grounding the wire nothing happens then the problem usually is a bad gas gauge. This of course, takes into account you have current through the wire to the gas tank.

Follow-up from Roger:

Is the sender a variable resistor?

Reply from Norm:

Yes, the sender works on the principle of variable resistance. That is irrelevant to the question. If you get no response from the gauge when the wire to the tank is grounded, it is clearly the gauge circuit and not the sender circuit that is being tested. The sender is a very straightforward device and it is easy to replace.

Question from Cary (1970):

The fuel, water temp, oil pressure gauges in my '70 LeBaron have completely stopped operating.  I installed aftermarket gauges under the dash, so now I can monitor the oil and water temp.  However, I still do not have a fuel reading (which is VERY important--the 440 burns a lot of gas, quickly).

Reply from Dick:

This is the old Gauge Regulator syndrome.

Question from Geary (1970):

Well, my gas gauge doesn't work at all, and every time I go out I pretty much have to estimate how much fuel I have.  My question is that, where would I look for the ground to the gauge to see if it has rusted off?  And if it has not rusted, what else could be my problem? 

Reply from Dick:

The most vulnerable location is back at the tank. The tank may or may not have had a separate ground wire on it, I don't know in the case of a 1970. Most cars just use the physical mounting straps and bolts to provide a ground for the tank, but the tank MUST be grounded to make the gauge work. You can always add a ground wire from the tank to the frame of the car - it must be clean and bright metal so you know the contact is good.

HOWEVER!!!!, your problem is more likely a bad fuel gauge sender, or a disconnected sender wire. Check that out first before you get all tied up in grounding problems. Take your test light or meter and verify that you see a pulsating voltage at the sender terminal on top of the tank (with the key on, of course!). If you do, momentarily ground that terminal to the frame of the car while someone watches the dash indicator of the fuel gauge. I'm betting it will leap off the pin and head for the full end of the gauge. Don't leave it grounded more than a few seconds, this is just a momentary check. If the dash unit responds as described, all your car's electrical connections are OK, and your gauge sender is not doing it's job. Reasons and suggested cures for this are:

1. Float isn't (floating, that is). Seal it or replace it. 2. Rheostat in sender has failed. Buy a new sender. 3. Sender isn't grounded. Ground sender to tank and tank to car frame (this is where we started).

As for likelihood of causes, now we are into the occult, but my guess would be the wire from the sender to the dash unit is disconnected or broken, probably back around the tank somewhere.

Question from Kevin (1971):

When I fill up my tank the gas gauge says I only have a 3/4 of a tank, so I have to do somthing to the sending unit? Any suggestions?


From Robin:

My car pegs the temp gauge most of the time and the fuel only goes to 3/4 when full. But I have noticed all the gauges acting a little funny once in a while and I am pretty convinced the voltage regulator for the instruments is playing with me. I am going to retrofit a new regulator from the electronics wholesalerthis spring for a grand cost of about a $1.00 or 2 and see what happens as per this article.

From Don:

It sounds like you need a better ground at the sending unit.

Question from Elijah (1971):

This weekend, I pulled the instrument cluster out of my '71 Imperial  LeBaron, and replaced several items, including a broken odometer and trip  meter, as well as a couple of non-functioning gauges. After I put it all back together, everything is working fine.  EXCEPT -- now, when I start the car, the alternator gauge swings wildly to the right (charge). And, when I drive, any small change in the electrical system, such as a turn signal, causes the alternator gauge to fluctuate quite a lot. Also, if I turn the lights on, the gauge shows a charge as long as I'm moving, but if I stop, it swings far to the discharge side.


From Dick:

Do you have a shop manual for the car? If so, look at the ammeter connections on the instrument schematic and see if the gauge is supposed to have an external shunt ( a wire connected from one terminal on the gauge to the other one). If the shunt is external, you must have knocked it off or broken the wire. If it is internal, it won't show on your diagram, and you will have to replace the gauge unit. The purpose of the shunt is to conduct the majority of the current around the gauge without running it through the gauge. If the shunt is not connected, the gauge will be hypersensitive.

After I signed off last night, I took the '72 manual and did a little more study. The shunt is contained in the main harness on the engine side of the firewall, and consists of a spliced connection between the red #10 wire and black #10 wire that come through the firewall on pins 16 and 25 of the main bulkhead disconnect. In 1972, this was called splice #3. See if you can identify it from this. If you can, unwrap it and inspect for poor connection, you may have to strip it all apart, clean everything, and resolder the splice. An alternate procedure, and probably easier for you, is to install a replacement shunt right on the ammeter terminals. It is a bit of a hipshot as to the size, but I would try a 12 inch length of #16 wire (stranded copper, of course, and solder the terminals on the ends of the wire, do not trust crimp on terminals for this) for a start, then see if the gauge is back to acting normal. If it is still too twitchy, shorten the wire. If it is really insensitive, lengthen the wire. This wire is going to get slightly warm, so do not bundle it all up in a ball and tape it, just let it wander around by itself in the open air. Do not ignore this problem, because it is affecting the alternator charging rate, and making everything electrical in the car overly sensitive to engine RPM.

From Frank:

I am pretty darn certain that your car, as my '72 did, uses an external shunt. The bad news is that I seem to remember that the shunt was in the wiring harness somewhere. I don't remember if there is overload protection in this circuit, but remember that the alternator's full output current is about 65 amps. If the engine is not running and you are drawing current, that also runs through the ammeter. (Figure about 20A for headlights, 15A for interior lights, and you start to get big numbers. You don't want to run this amount of current through the ammeter, something will eventually voice its displeasure. I had a '73 shop manual somewhere and I just can't put my fingers on it right now. I'll need to look over at Dad's house. Try to go back over what you did when working on the dash, to see if that provides any clues. Also, did the meter work before?

From Dave:

First, make sure that your instrument cluster is grounded properly...automotive electrical systems do really wild things if ALL of the separate ground wires aren't in- stalled where they belong. Also make sure that both wires are snugged up on the back of the ammeter, loose connections here will cause these problems and others. Second, remove the voltage regulator from its place on the inner fender and clean the spot where it is mounted, as well as the screws and the base of the regulator it- self. The regulator must be well grounded too. Third, make sure that all wiring attached to the alternator is tight and corrosion- free. Be careful if you decide to remove and clean these, since the large red wire with the ring terminal is the alternator output and is connected directly to the positive side of the battery...remove the ground terminal from the battery to prevent fireworks in the event that you accidentally ground any terminals while you are cleaning them. Fourth, loosen the belt on the alternator and try to move the shaft from side to side. You shouldn't be able to! If you can, then the bearings have gone bad in the alternator itself and will have to be replaced. This will also cause the symptoms that you are describing.

Question from Mike (1972):

Why is their two engine oil sending units on my 72 LeBaron? 1 big bell type and 1 smaller one for the oil light?


From Elijah:

One sending unit is for the actual oil pressure gauge (the large "bell type" unit mounted behind the intake manifold) and the other is for the "Signal Sentry" light on the dash.

From Al:

The big bell type works the pressure gage. The other one works the no oil pressure light.

From Steve:

The "big bell" type is for the gauge. ...and you are right,the smaller one is for the light.

From Dick:

All Imperials, at least back to 1967, have both a light AND a gauge, strange as it might seem to you. As is typical for Imperial, they wanted to do thing right! The light is the "gauge sentry", which lights to warn you to "check gauges" when any of the dial type gauges are out of their normal range. In the case of the oil pressure senders, there are two of them on each car.

From Chris:

My '72 has both, the smaller one for the "idiot light" and the larger, bell type for the gauge...

Question from Wayne (1972):

I recently purchased this 75k beauty, and everything (including AirTemp II) works great, except for the gas gauge. The former owner told me it wasn't working, and for the last couple of weeks, I have been just running it 100 miles or so and topping it off, using the trip odometer. The "Check Gauges" light has been on constantly. Well, today something weird happened. I looked at the gauge and it was registering. It was showing about 1/2 full, which since I had filled it up just 60 miles before, I didn't believe. So, I took it to the gas station and topped it off, it held about 4 gallons. Back on the road, the check gauges light came back on for awhile, and then the gauge cut back on, and went to 1/2 again, where it stayed for about a 60 mile round trip. What's up with that? Is it the sending unit, or the receiving unit?


From Dick:

Most likely this is a failing moveable contact inside the sending unit. You can take it apart and clean everything up, and check with an Ohmmeter - the resistance should vary with arm position from something around 10 Ohms for full to 60 Ohms when empty. These values are not critical, anything within + or - 30% will make the indicator behave pretty well. If the sending unit doesn't check out at those values, you'll need to replace it. Attempts to reattach the internal wire and wiper contact are usually very frustrating.

From John:

I had a problem like this on the first 69 LeBaron that I owned. It seemed to only happen in very hot weather. Sometimes when using the power door locks, this happened. It happened many times. Disconnecting the battery for a while made it go away. I never did find out what caused it. so far, this hasn't happened to the one I own now. When the lights were stuck on, pressing the power lock button would make sort of a sick sounding buzz. most likely from the relay.

From Stevan:

Have you tried checking the oil level?  I have a 72 imperial and when it gets one quart of oil low the "check gauges" light comes on.

From Elijah:

First of all, it sounds like the "Check Gauges" light is functioning properly. As part of its duties as your Signal Sentry warning light, it is supposed to come on if the gas gauge falls below 1/4 tank. So if the gauge has been reading empty all the time, the light should stay on. So why doesn't the gauge work? The most likely culprit is behind the dashboard where the wire from the gas gauge sending unit (located in the gas tank) connects to the instrument cluster. This wire has a round connector that connects to a post on the back of the instrument cluster. This connector often becomes loose over time, which means you have a poor connection -- resulting in a faulty reading at the gauge or no reading at all. The loose connection will also allow a build-up of corrosion, which results in no reading at the gas gauge. From the symptoms you describe above, this sounds like a possible scenario. You can easily fix this problem by disconnecting the wire and cleaning the connector and post. It would also help to *gently* squeeze the connector closed a little bit so that you will have a nice snug connection. The only problem is that this connection is buried pretty far up in the dash, and can be hard to reach. I've always been able to do it, but I'm tall and thin, so I have long arms and narrow hands, which is a big help. Nonetheless, I think that if you drop the panel where your Vent levers are (beneath the steering column -- held on with four screws) and then drop the black A/C vent tube (carries air to your left spot cooler -- held on with one screw), you can probably reach the connection. If you don't have a shop manual, I would be glad to copy the relevant pages from the '73 shop manual (I don't have a '72, but they're virtual identical). Two other possibilities are 1.) you have a bad sending unit in the gas tank, or 2.) you have a loose connection at the sending unit. However, I've had two '71 Imperials which both had this problem at the instrument cluster connection, so I'd be inclined to check there first.

Question from Philippe (1973):

A friend of mine has a '73 2dr Imperial and the "check gauges" light remains always "on". I don't know the "modern" Imperials, what is the purpose of this "light"?


From Steve:

This light will come on when any of the gauges read low. When it lights up, it's pretty hard to miss. The one in my 1971 is on when you first start the car and after the gauges all come up, it goes off.

From Elijah:

The purpose of this light is to warn the driver if anything is wrong with the car. If any of the gauges -- temperature, oil pressure, fuel, or alternator -- go outside of their "normal" range, this light will come on to get the driver's attention.

If your friend's Imperial is below about 1/4 tank of gas, this light will come on.

Question from Chad (1973):

Every once and a while the gas gauge on my 1973 Imperial stops reading and the needle goes to the beyond full area so that I cannot read it. While it would be nice to have a mysterious free gas source in my Imperial, I don't think that is what is happening. Is this a problem with the wiring at the sending unit, maybe a bad ground or could it be the sending unit or the actual gauge? It usually does it after I start the car but will fix itself in about 20 or 30 minutes of driving or when I restart the car if I haven't been driving that long. Any ideas?


From Dick:

If it is going beyond full, a good bet is that there is a bare spot on the wire from the tank unit to the dash unit. It could be anywhere, including within the wiring channel through the body. The best way to fix this is to replace the whole wire from the tank unit to the dash unit with a new wire, unless you get lucky and find the area with the insulation worn off.

Reply from Chad:

Should I inspect the wire that goes from the sender to the gauge for a possible short (exposed wire)?

Answer from Dick:

If your gauge sometimes shows OVER full, yes. If it just fails to operate sometimes, there is some other problem.

From Mike:

If you have a poor ground connection (likely because the ground rusted away) or, possibly a bad tank sending unit. If the problem is sporadic, I'd suggest the former. Decade and score-plus old electrical connections are always suspect. Clean, Vaseline, and reconnect.

Reply from Chad:

I will have to get under the car and take a look. I was just hoping that I wouldn't have to venture under the dash as I hate moving things around under there as they tend to stop working sometimes when something gets knocked loose. Where is the ground, grounded? I thought there was only one wire that went to the sending unit and this was the same one that connected to the gauge?

Reply from Dick:

Sorry to be a pain in the butt here, but if the tank grounding or the sender has failed, the gauge will go to zero, not over full. OVER full indicates a short to ground on the sender wire.

Question from Frank (1973):

My temp gauge within the first 10 minutes of running goes directly to the far right hot section. However, car is not running hot, as I've had the
actual temp checked several times.  After it reaches that, it comes back to about 2/3's.  Previous owner told me to disregard and I've never had any

Reply from Elijah:

Sounds like a faulty sending unit.  The sending unit is pretty conveniently located toward the front of the engine, so it's easy to replace.  The last time I checked, Napa had the exact part.

Question from David (1973):

Does anybody know what triggers the "check gauges" light on a '73? I almost had a meltdown a week ago it should be easy to find one that switches at a lower temp. Is it the same as with the oil pressure?


From Leslie:

I'm not positive on your '73, however on my '67 sedan there is the gauge sending unit in front of the water pump housing off to the right side and I believe the check gauges switch is on top of the water pump housing pointing upwards with 2 wires attached. And like yours my "check gauges" light did not light up when I went into meltdown this past weekend on the way to the WPC Portland meet. I did learn that driving my car on the freeway at 80 mph for 2 hours with rusty coolant in cooling system is why I had meltdown. So now that I have thoroughly flushed my heater core, engine, and radiator I no longer have rusty coolant.

From Elijah:

For Imperials with the Signal Sentry System, there are actually TWO sending units for temperature, and TWO for oil pressure. The two temp units are located at the front of the engine block -- one is large and round, with two wires to it, and is located next to the thermostat housing. The other is a simple switch (for the Signal Sentry), and is located below the first, facing forward from the block, with a single wire to it. The oil pressure sending unit is a large affair at the back of the block, behind the intake manifold, with a single wire, while the switch (again for the Signal Sentry) is a much smaller unit, also located at the back of the block, again with a single wire.

Question from Terry (1973):

 The gauges in my 73 have some problems that I am planning on addressing soon. 1. The temp gauge simply doesn't read, I strongly suspect the sending unit under the hood 2. The oil pressure gauge reads very high, I am not sure what causes this, but the car is not overfull of oil. 3. the gas gauge is erratic and never seems to read full...

Reply from Elijah:

On the back of the instrument cluster, there's a big round plug-type affair which has about 8 electrical connections. This connector includes the wires for all gauges except the gas gauge. I'd suggest pulling the plug ;-> and checking for corrosion or a looseness of the individual copper connectors. You can tighten these connectors by using a pair of needle-nose pliers to CAREFULLY and GENTLY squeeze them closed a bit. I'd also suggest electrical contact cleaner to clean the connections.

Question from Terry (1973):

I recently replaced the oil sender unit on my '73. The unit I got from NAPA was too large in diameter, but a pipe nipple and 45 deg elbow fixed that!  It now works better, but I am not sure where it should run. Now the oil pressure needle seems to be a little over half way to the "H" side. Is that "normal" for these cars? The car sure seems to be running well. It is such a joy to sit at a stop light and she just PURRS! I love it!


From Dick:

The electrical gauges are kind of a joke anyway, as far as accuracy goes. I would not ever trust an electrical dash gauge for other than telling you if you have a sudden drastic change from what you are used to seeing. If you want to know what your oil pressure really is, the thing to do is to get a real (mechanical) oil pressure gauge and tee it into the fitting where the sender is. You can do this temporarily, or leave it there so you can check it from time to time. The fitting will be 1/8 inch pipe thread (I know it looks MUCH larger, but pipe goes by the internal diameter). Normal readings are given in the shop manual, which I do not have in front of me, but anything over 10 PSI is going to be OK as far as not causing engine damage, and a new engine would run 50-60 PSI on a cold start, settling down to about 40-45 at road speed, and 30 or so at idle. But after 100,000 MI, these numbers will all be about 30 to 50 % lower. As I say, don't worry as long as it never gets below 10 PSI even hot, at idle. Bottom line is, if you don't hear the lifters clacking, you're probably OK, the 440 is as close to bulletproof as they come. 

From Bryan:

All the big blocks I've dealt with have a plug right next to the original oil pressure sending unit that also goes to an oil passage. Instead of putting in a tee fitting I would put the fitting for the mechanical gauge where the plug was. Makes for a better looking installation.

From Elijah:

The optimum gauge reading for the '71 to '73 oil pressure gauge is indeed just a bit towards the "H" -- so yours is perfect, Terry! 

L *-----------* H 

          ^     ^          As long as you're somewhere in that range, things should be good. 


C *-----------* H  

      ^ ^                   And this is about optimum for temperature -- preferably right on the first "*".   

Question from Matt (1975):

My gas gauge shows empty and the red light comes on but tank is full. My neighbor says it is the float since the red light works. My service manual is MIA (wife moved it) so how do we get the float out? Drop the tank or is their access from the trunk. The tank is full as I thought it was empty and was filling it up and the shutoff stopped it at 10 gal. At 8 mpg, it would take about 200 miles to empty?


From Mark:

First I'd make sure the tank has a good ground. I had a '76 Dodge where the gauge quit working and ran a jumper ground wire to it and the gauge worked fine. I believe the low gas light was also on when this happened.

From Brad:

The sender is on the right side of the tank pretty much half way from front to back. You can do it without dropping the tank as I have done so a number of times. You might have to drop the right side exhaust pipe to gain access. Before removing the sender, check the grounding strap that should run from the metal fuel line on the sender to the metal fuel line mounted on the frame. You can construct a temporary strap from some wire to test if this is your problem. If you need to remove the sender, you'll have to run your tank almost down to 1/4 before taking the sender out. To remove the sender lock ring, I just use a large standard screw driver and a hammer. Just remember to get it back in place properly or it will leak.

1977 Service Manual Page 84  Page 85  and Page 86

Question from Lorne (1975):

I was just wondering if anyone has experienced the problem I am having with the gas gauge on my 75. It started when I filled it to the top of the tank, for an out of town trip to Edmonton. The tank registered full and dropped normally during the trip. Upon arrival, I still had about half a tank, which is normal for that trip from here (Calgary). I filled up again to the top for the return, and again arrived home with the tank about half full. I drove around town for about a week on what seemed to be a bottomless gas tank as the gauge dropped ever so slowly throughout the week. Finally one day on the way home from work, it stalled as I was doing about 70 km/h down the road. The gas gauge still read 1/4 full and the low fuel light hadn't even come on. Thinking I had really blown something, it took me a while in the middle of the turn lane of a major intersection, to realize that I was somehow out of gas. After trying the great idea of putting a couple of liters in, the old girl fired right up, much to the glee of the people stuck behind me for the last 20 minutes. Anyway, I then went to the gas station and again filled it up. This time the gauge went way past the full mark and out of sight into the right side of the gauge. It now comes down to about the 1/4 mark before it starts to give me an indication that it needs gas. I don't normally run it that low, but I wanted to see if maybe the float was stuck and would drop down if I ran down the tank again. The gauge now seems stuck within these parameters and will not function normally. I miss my little red light telling me I have only got 1/4 tank left. It won't seem to drop below that level. As I just hate the thought of running out of gas again, and I was wondering if anyone else has had this problem, what it is, and if they may know how to fix it. Any and all help would be appreciated. Note that the gauge worked perfectly until that fateful fill-up.


From Frank:

Chrysler gauges work by measuring a varying current. A variable resistor acts in the sending unit to vary the current. So put some power to a varying resistor and measure the current. The measurement is proportional to the input of the sending unit.... AND of the supply voltage. (Remember Ohm's Law: "Ohm, Ohm on the range, where the deer and the antelope play..." Oops wrong ohm. rather: "E-I*R") I'm simplifying the circuit some, since total system resistance also plays a part, but I'm ignoring that since it should be negligible, and in this situation, does not matter anyway.) Problem is, in a car, you can't always guarantee exactly 12V supply. Here's why: First of all, a fully charge lead/acid cell produces 2.2V. There's 6 cells in a car battery, thus 13.2V. So there goes our 12V supply. You can't charge a battery, unless you charge w/ a higher voltage. The higher the voltage, the quicker the charge. Thus when the engine is running you see about 13.5-14 V. And now further away from 12V. When it is hot, the electronic voltage regulator reduces the charging voltage to decrease battery heating. And now we can't be sure exactly, what the voltage will be at any time. Plus, under high current usage, the voltage may sag when at idle. Well! Since there is not a steady supply voltage, Chrysler puts a voltage limiter in the circuit. The limiter is a weird device. (Or at least to this semi-conductor oriented guy) Inside the case of the VL is a variable resistor and a heating element wound around a bi-metal strip. When the voltage is high, the heating element warms the bi-metal, causing it to move along the variable resistor, dropping the voltage. If the voltage gets too low, the warming is reduced, so the bi-metal moves the other way, increasing the voltage. You already have guessed what the problem is by now. The voltage regulator is out of calibration. I believe that output voltage from the limiter is around 5V. You can test it and see if the output from the voltage limiter is too high. BTW I think the same device is also connected to the coolant temperature gauge.

From Robert:

>You already have guessed what the problem is by now. The voltage regulator is out of calibration. I believe that output voltage from >the limiter is around 5V. You can test it and see if the output from the voltage limiter is too high. BTW I think the same device is also >connected to the coolant temperature gauge. 

In a word, NO. At least not on a 75. The voltage limiter does attach to both the fuel gauge and the temp gauge, but it either works or it doesn't. When mine went south it was accompanied by a very noticeable puff of smoke, momentary pegging of the gauges, then zero reading. The gauges weren't quite as accurate after replacing it, but at least they didn't go up in smoke too. Quick gauge/wiring/limiter test: 

>From under the car, disconnect the blue wire attached to the fuel pickup/sending unit, gauge should read empty and low fuel light >should come on. 

Connect the wire to a good ground, gauge should read full. Same test applies to temp gauge and oil pres. gauge/lamp.

From Jay:

The fuel gauges in both our '62 and '66 work consistently, but read lower than what's in the tank. One is down a couple of gallons, the other reads a percentage of what's in the tank. With these behaviors, there is no risk of running out of gas if I watch the gauge. I still like to go as far as possible on a single tank so I spend as little time as necessary stopping at filling stations. Since I don't trust my gauges 100%, I use the trip odometer to judge "how many more miles I can go" before I have to stop for gas. If your trip odometer and speedometer work okay, I would recommend that you always top-off the tank when getting gas and set the trip odometer to zero. 

Depending on which car I'm driving and what kind of driving I'm doing (city or highway), I can reliably go 220 miles city (roughly 9.5 mpg) or 320 miles highway (roughly 14 mpg). You may have to study your gas mileage over several tank fulls of varying driving conditions in order to get a good idea of your range is on a full tank. My estimates are for an Imperial w/23 gal tank, that gets from 10 - 14 mpg. Of course this is a "temporary" measure until I can get both gauges working properly, but it works for me. Always a good idea to keep a couple of gallons in a can in the trunk, just for peace of mind.

From Robert:

More than likely the sending unit in the tank is the problem. My 75 acted erratically for a while, then went to full and stuck there, until I replaced the sending unit. If you slide under the tail and trace the fuel line, you'll also see a metal strap about five inches long clipped in parallel to the rubber fuel line connecting the tank line to the steel body line. This is part of the ground for the gauge and could be almost rusted through because of all the road salt, but I doubt it. The service manual claims you need some fancy gadget for popping the retaining ring (for the sending unit/pickup assembly) off the tank, but a screw driver, small hammer, and light taps work just fine. The tail pipe is often just slightly in the way. If so, unbolt the hangers (where they attach to the body) at the bumper end and in front of the axle. How's the heater core??

Question from Steve (1981):

My '81 Imperial oil pressure light came but the oil is up to level. I hear tappet noise and my car sat for about three weeks. Help!!


From Dick:

This (no oil pressure coupled with valve lifters suddenly ticking) is a very serious situation. Either your oil pump is not pumping or you have a spun bearing. Either way, you have to drop the pan and take a look at things. Do not run the engine at all until you do this. If you're very lucky, you'll find the oil pickup float has fallen off or the screen is blocked. More likely, there is a spun bearing - since you don't hear any rod knock, it is most likely a main bearing. While you may be able to patch this up and get a few more miles out of the engine, the right way to do this is to plan on a complete engine rebuild. Sorry, this is bad news (unless, like me, you enjoy rebuilding engines!)

From Joe:

Dick is right about dropping the pan, but I would like to add another reason for no pressure. Your Imperial uses the 318 - the distributor gear in this and other Chrysler V-8's are driven off the camshaft - the distributor's shaft fits in a slot on the top, and a hex shaft going to the oil pump on the bottom. Although rare in a relatively low-stress application such as this, the hex shaft has been known to strip, or more commonly, break off at the pump. My guess is some form of debris might have found its way between the inner & outer rotors of the pump(not much clearance in there) and when you started up the engine, this particle jammed the rotors and the shaft twisted off. Freak thing, but possible.

In addition to checking the things Dick told you, pull the distributor(mark it's position first!) then, noting it's position as well, pull out the distributor gear. If there's no hex on the end, that's your problem. If you don't check that gear, AND your oil pump, you won't cure your problem. My suggestion, while you have the oilpan off anyway, which is necessary to get to the pump-located on rear main bearing cap-take the oil pump off, DISASSEMBLE it and CHECK it for debris, wear, burrs on the rotors, and clearances between inner & outer rotors. Checking these things will ensure everything working right upon re-assembly.

From Jeff:

Many times the shaft shears off at the very bottom tip area. The camshaft still turns the rest of the shaft, including the top half which turns the distributor.

I have seen it happen several times on 318s, curiously the ones I have seen have all been early '80's units. I have found that a large piece of debris gets into the pump and locks it up. The shaft then shears.

So, even if that is the problem: sheared oil pump drive shaft, the oil pump & pickup will need to be replaced. If the debris somehow dislodged after the shaft sheared, you could get lucky, but I would expect the oil flow to pull it back in.

From William:

The oil pump shaft on my '81 LeBaron sheared off a few years ago. It ran for about 15 seconds after the light came on (70mph on the freeway) as the broken oil pump shaft does not interfere with the engine running. After removing the pump, it was in fact seized, it appeared to be from many years of small debris packing into a thin film in the corners of the rotor (valve seals probably). I replaced the pump and shaft, thinking I was pretty clever. I checked the main and rod bearings, they seemed ok, so I fired it up. Still no oil pressure. After a frustrating weekend of trouble shooting, I traced it to a spun cam bearing, blocking oil flow. I just junked the motor and dropped in a hot 360. Anyway, might be food for thought.

Question from Stan (1981):

I drove my '81 Imperial to day and my dumb temperature light came on very slightly then got brighter and brighter then went off then came back on and stayed on. Where do I start? Could be the T-stat, Fan clutch, Rat. What do you think are could be just a bad sensor?


From Rich:

You might want to start with checking to see if you have any anti freeze in the radiator if so then run car and see if thermostat is opening. If that is fine and car is not over heating then I would say it's the sending unit.

From Rob:

Be careful with this one. I just found out that even though my sender works fine, it won't go on if there is no coolant. After I (hopefully) blew my head gasket, fixed the leak and refilled the radiator it comes on like a charm. I highly recommend hooking up a real gauge. At least temporarily until you find out what the problem is. Without a gauge it will be hard to tell the effects of any change you make. Especially since your light isn't always on and the by the time that idiot light comes on you are in definite danger of overheating. If you want to check it, the sender is behind/under the a/c compressor. Easy to see, hard to reach. 

Question from Jeremy (1981-1983):

I am really beginning to question the accuracy of my digital fuel gauge. It will fall from 5 gallons to 2 gallons almost immediately. Maybe it is my imagination. I don't know. Has anyone else had this sort of problem? With the exception of the U-joints and front shocks, everything on this car is original. I have never had any problems with the digital dash. The car is still fuel injected. It runs well, with occasional hesitation and low idling. I have owned the car for 5 years and I don't ever remember the fuel gauge being quirky.


From Dick:

The unpredictable nature of the fuel level indication is part of the charm of these cars. They often perform unusual and random changes without necessarily meaning anything, I have just learned to trust the trip odometer and refill when I think I have used up about 10 to 12 gallons. Sometimes the gauge agrees with the facts, and sometimes it doesn't. All 4 of my cars exhibit the same schizoid behavior.

From Ed:

My 81 and 82 exhibit OPPOSITE fuel inaccuracies. The 81 tends to read a bit higher than actual and the 82 a bit lower than actual fuel remaining in the tank. The 81 in particular will read unusually HIGH when first started up, then the gallons will quickly count down in a minute or so to closer to actual, particularly when the tank is getting low. It has always performed this way, so I guess I'm just used to it.

From Bob:

The problem is likely in the tank sending unit.  Had mine out last summer, found a "last' MoPar replacement in Brooklyn, NY, installed it and adjusted it with an ohmmeter while a helper read the digital values. If you want to try a new sending unit, let me know and I'll dig up the resistance range for the sending unit. There is probably nothing wrong with the instrument panel. It is a time consummating effort, the  replacement may be difficult to obtain; there was a change in early '81, is a function of when you car was manufactured. A unit from a conventional carburetor equipped car may work, I'm not sure right now.

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