The Stovebolt Site Forums The Shop Area The Electrical Bay fuel gauge peggs out past F.

my 66 chev p.u. still uses factory gauge problem is it reads past full.useing a test light starting @ back of gauge white + wire shines bright.tan- wire barely lights up test light all the way to sendind unit sender was pulled for a visual inspection it looks fine.all grounding straps were pulled filed clean and re-installed.the omly time i can get the gauge needle to respond is when i use a jumper wire conected to sending unit + stud and grnd it to the - wire just above the fuel tank inside the cab. what gives?

You are not grounding through the sending unit. If you toucg the wire to the ground and the gauge goes to E then the problem is in the sending unit or it not grounding properly.

ok, i'll pull it out tomorrow look at it more closely.i had it out sat.looking at it did'nt see anything suspicious the flat black wire was anchored down solid but maybe something is going on inside that rheostat box i did'nt see the first time. the 18 ga. black grnd wire on top of the sender grnds to the inside cab wall.so if thats not the problem then it must be inside the sender itself.correct?

Likely. The way the gauge works is the power comes from the gauge and goes to the sender. The sender is grounded and depending on where the float level is determines how much is being grounded.

Usually when a fuel gauge on these old trucks goes past full and stays it's because the ground is bad. Could simply be a bad connection, or could be a bad sender. May also have a bad wire from the back of the gauge to the sender. One way to test that is to put a test light at the end where it connects to the tank. Disconnect the wire at the tank to test with the light.

If the wire is good, the test light will act as resistor and the fuel gauge should come back towards empty. You could just touch the wire to a ground, but you have to be careful you don't just hold it there or you could burn out the gauge.

i tested the wires behind the gauge useing a test light.the white wire causes the test light to glow bright.i follow the white wire as far as i can testing it along the way until i lose sight of it or can't reach it anylonger,always getting a bright light. the tan wire however has a dim glow to it from the back of the gauge to the fuse box continuing to the sender. the only time i get a reaction from the gauge needle is when i use a jumper wire conecting one end to the sender stud the other end to the grnd wire just above the tank.then the needle reads just above empty say 1/8 of a tank.that can't be correct because i know for a fact there is at least 2/3 of a tank of fuel in there.

When you take the jumper wire and go from the stud to ground you are bypassing the sender inside. You won't get an accurate reading of what is in the tank because the resister inside the tank is no longer part of the circuit. Eventually the gauge would go to empty doing that.

Sounds like you have located the problem, the sending unit inside the tank is not working. Now to pull it and see why.