Gas gauge not working

[mc1984ss]

First off I have the tank out of the car and have a brand new sending unit. The new sending unit is functioning properly, I checked it with an ohm meter. I also verified that the pink wire ( gas gauge wire) running from the back of the car up to the fuse panel is not broken. I have continuity from one end to the other.

I mocked up the new sender just to verify that everything was working and it's not, the gas gauge stays pegged. I pulled it apart yrs ago and it worked then. Any idea where to stay looking? I tried grounding the pink wire to see if that made a difference and it did not. Thanks in advance

 

[79 USA 1]

Check your ground wire inside the trunk, drivers side near the drop off. The wire may have corrosion under it or may have broken off.
Just a starting point to look.

 

[mc1984ss]

Ground is good, I even added an auxiliary wire to be safe

 

[g0thiac]

First off I have the tank out of the car and have a brand new sending unit. The new sending unit is functioning properly, I checked it with an ohm meter. I also verified that the pink wire ( gas gauge wire) running from the back of the car up to the fuse panel is not broken. I have continuity from one end to the other.

I mocked up the new sender just to verify that everything was working and it's not, the gas gauge stays pegged. I pulled it apart yrs ago and it worked then. Any idea where to stay looking? I tried grounding the pink wire to see if that made a difference and it did not. Thanks in advance

So I've dealt extensively with these issues, and can say the fix will depend on if the gas gauge is functional itself first, and also where it's at, below E or above F.

First, check your grounds on the tank. If there's rust there, unbolt the black wire, wrap some wire around the O ring temporarily and run it to a unpainted spot on the frame where you can stick it behind a bolt as temporary ground. But if you can, try sanding down the spot where it originally was, until you see unpainted metal, and just use that.

The S wire, or "Pink" wire as you call it, should be receiving 12 volts. Checking continuity is smart, but it's sometimes always isn't enough. It's not an indicator on whether or not it's receiving proper current.

If changing your grounds don't work, then your next step would be to check the gauges itself. On my Pontiac, there were two culprits I suspected.

First is the black plastic connector. Sometimes the brass contacts on there, become corroded, or even bent out of alignment. You can try carefully, bending the top ones slightly up, and the bottom ones down, in order to ensure proper contact.

Or, you may be like myself, and the traces will be f**ked up on the PCB. My Instagram page below, shows a video tutorial on how I fixed it.

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[mc1984ss]

Awesome thank you very much. Grounds are great and I have a perfect connection at the wire in the trunk. I ran a auxiliary ground and even disconnected the bullhead connector in the trunk and tried hooking up to the pink wire there. So the pink wire should have 12 volts????

 

[mc1984ss]

Also my gauge is pegged to F maybe past

 

[g0thiac]

Also my gauge is pegged to F maybe past

If it's past F, it means it's not getting the correct 12 volts yes. You probably do have a good ground. My Pontiac used a tan wire however as opposed to pink.

What I had to do, since mine did the same after a new sending unit, was cutting the wire coming out of the tank, and running a 10 foot jumper cable, all the way to the dash, and soldering it directly to the back of the fuel gauge, because my PCB traces were no longer good.

Before doing that however, take out your gauge cluster and inspect the black plastic connector, and also the traces on the back of the fuel gauge.

If you suspect a connection issue after trying what I told you, cut the wire coming out of the sending unit, wrap some electrical cable on the one end, and run the other back all the way to your gauge, turn the key on and touch it to the metal part of the back of the fuel gauge, like mine shows with the orange wire in the picture- before deciding if it needs soldering.

If it works, you will need to either spend time figuring out where the break is in your harness. Or, do what I did, and run it behind the tail lights, through the trunk, into the back seat and under the carpet, past the front seat and behind the dash finally.

Unless the sending unit isn't connected properly, that could be an issue as well tbh.

 

[mc1984ss]

The pink wire that connects bro the fuel sender plugs into the lower left corner of the fuse panel (along with the tailight wires) do you know from here how power heads up to the gauge cluster?

 

[g0thiac]

The pink wire that connects bro the fuel sender plugs into the lower left corner of the fuse panel (along with the tailight wires) do you know from here how power heads up to the gauge cluster?

It goes from the fuse box to the plastic connector in the dash.

If trying a different ground didn't work, like I said, remove the gauges and make sure the connector and traces on the circuit board like in the photo I showed are good.

And if that doesn't work, then try running the long wire from the tank, and tape it against the metal part of the gauge while the car is running.

Because I guarantee that if the sender unit works good, then cutting the wire coming out of the tank, twisting it on to some 10 ft wire, and trying to touch to the back of the fuel gauge will make it work. Don't worry about the tail lights or any of the existing wiring, you need to bypass it.

That's all the advice I can give.

 

[bracketchev1221]

I’m in the same boat with my 70 and I think it’s the gauge. There is a resistor on the back of the early gauges. Not sure on the newer gauges. But I’ve tried 2 new senders and an old one I had and they all read wrong the same. So only thing I have left is check the gauge.