1968 442. Fuel gauge has always worked until recently. It is now pegged past the Full mark, closer to the 3:00 position on the gauge. It moves slightly when the ignition is turned on. Is this an electrical/grounding issue or more likely with the sending unit?

 

This is the classic sign of an open circuit. Check the sending unit ground connection and make sure it is connected, clean, and tight. If that doesn't fix the problem, separate the connector where the wire from the sending unit connects to the wire from the front of the car. This is usually behind or around the license plate area. Then ground the wire coming from the gauge and turn the key ON. The gauge should go to E. If it does, the gauge and the wiring from it to the back of the car are fine and the problem is most likely the sending unit.

 

x2 with above.

 

Yep. I have the same issue with my 71, and had it as well with my 70 back in school. I found on the 70 that the push-on connector terminal at the pickup was loose. Crimped it with pliers and never had a problem again. On the 71 I got too lazy in my old age, so I haven't dropped the tank to fix it - I just reach behind the license plate and wiggle the brown wire until the gauge works again.

 

I've got the same issue with my tail lights, been to lazy to splice in a replacement harness I have on the shelf. I feel like Pa Kettle...

 

I have the same issue with my 69 442. My pegs over F when full and when the gauge gets to about 1/2 tank is empty. The gauge needle also fluctuates some when the tank is closer to empty. So I followed why Jaunty75 wrote and cleaned up the ground and no change. I then separated the connector, grounded that and it pegged even higher than before. So if I did it correctly and am reading this right, problem is with my gauge and not my sending unit ? I was getting ready to drop the tank, but now not sure. Thanks.

 

This is not the same issue. Your gauge actually works. In the OP's case, his gauge goes way past F and stays there whenever the ignition is ON no matter how much fuel is in the tank. Your gauge actually reacts to the amount of fuel in the tank, even if it isn't pointing where it should. The needle fluctuating when near empty could just be the fuel sloshing around in the tank. There are baffles to minimize this, but perhaps one of them has broken off in your tank.


Grounded what? When you separate the connector, you're holding two wires. Which one did you ground? The gauge should go to E when the wire coming from the dash is grounded. If there is a break in the wire between the dash gauge and the rear of the car, then the gauge would go way past F as there is an open circuit. It sounds like you grounded the wire coming from the sending unit, which wouldn't show anything, and left the wire coming from the gauge disconnected, which would be an open circuit. Make sure that it's the wire from the gauge that you're grounding and that the gauge does actually go all the way down to E when you do so and the ignition is ON.

Assuming your gauge does actually go to E when grounded, the bottom line is that your sending unit works and your gauge works. The problem is that the gauge isn't pointing where it should. This could be because the sending unit isn't working properly. It could be because the gas gauge on the dash isn't working right. If the sending unit has never been changed, it might be worth doing so as the rheostat may no longer be delivering the resistances it should at various positions of the float. I would suspect that before I suspected the dash gauge.

On the other hand, your gauge does work, albeit imperfectly. You just have to know what the positions the gauge points at actually mean and fill the tank when the gauge gets near 1/2. Not a perfect solution by any means, but it is functional, and there's something to be said for not having to drop the tank.

 

Sorry you are correct, my situation is different. I finally got back and redid the check again. I did have the correct wire and correct side the first time, but do not think I got a good ground. When I did it again today it went to E. I have had the car for 17 years and have never changed the sending unit so guess it's time. I have been living with the bad reading for a few years now, but last year I thought I had enough in the tank but ran out of gas when going to a local show. So time to fix it. Thanks for the help !

 

Further, I filled the tank this past weekend, and when the ignition is off, gage read about at F. But as soon as I turn on the ignition, it pegs right. I drove the car and now when off reads about 3/4 which is about right. Maybe related I have issues with my taillights. Brakes, signals and flashers all work except when I turn on my lights. Lights do work, but then don't change if I brake, etc. Since all part of the same harness , do I have a ground or some other wiring issue? Would a bad sending unit affect the taillights ? I would think not, but looking for advice. Thanks.

 

What the gauge reads when the ignition is off means nothing, and it's just a coincidence that it moves to where you would like to see it. The key thing is that, when the ignition is on, the needle pegs to the right. That's a classic symptom of an open circuit. Regardless of what you have done, you have an open circuit in your fuel gauge electrical line.


There is no connection between the workings of the fuel gauge system and other electrical circuits and components on the car. It is its own separate circuit.

One thing you have to do. Disconnect the sending unit from the wire from the front of the car where the two join in the rear of the car and ground the wire coming from the gauge. Then turn the ignition on. The gauge should peg on E. If it does this, the gauge itself and the wiring from the front of the car are in good shape and not the problem.

Please do this basic test before doing anything else. Troubleshooting the gauge system must be done systematically, not haphazardly by seeing what happens with different amounts of fuel in the tank, seeing where the gauge goes when the ignition is off, or checking the wiring of the taillights. The gauge system is a simple electrical circuit, and it should be possible to track down the source of your problem in short order.

Step 1: check the ground connection of the sending unit. Make sure it is clean, attached, and tight. If that doesn't solve the problem:

Step 2: perform the test outlined above. If the gauge goes to E, the problem is either in the wire from the sending unit to the connector or the sending unit itself. If you can access the top of the sending unit where the wires attach without dropping the tank, check that both the ground wire and hot wire are firmly attached an unbroken along their length. If you can't access the sending unit without dropping the tank, you'll obviously have to drop the tank to get at it.

If the gauge does not go to E, then you have a problem in the wiring from the gauge to the rear of the car which will have to be tracked down.

Step 3. if all wiring checks out and the dash gauge is ok, the only other possibility is the sending unit itself. Time to replace it.

 

This should be a brown wire that goes through a hole in the trunk near the license plate area. There is a connector near the hole/grommet that you can unplug to do the grounding test.

 

Thanks, I did not think they were related, just coincidental. I have a different issue with my taillights that I will address separately.

I did disconnect, cleaned up and retightened and no change. If anything it pegged to the right higher than before.

I did do this test, gage does go to E. I have not looked at wiring to the sending unit yet, but don't think I get to without dropping the tank.

Guess it's time. As I noted in previous post it has been I have never touched it in 17 years.

Thanks for the detailed steps. Looks like I have a winter project.

 

If you didn't drop the tank, how did you disconnect and clean the ground to the sending unit?

Anyway, since the gauge pegged E when you grounded the wire from the front of the car, it is likely the connection to the sending unit is open. That's what the issue was on my 70: the push-on connector was loose on the sending unit stud, and crimping it slightly so it fit tightly cured the problem.