My son said he went home for lunch and when he got back to work the gauge was over full, he said it looked like the fuses were OK any Idea what is causing this?

1970 Cutlass S

 

Yup.

You have a broken connection between the gauge, the sender, and ground.

Here's your fuel gauge circuit:

+12V (Instrument Power) ------> Fuel gauge (Driver's side + terminal) -----> Fuel gauge windings -----> Fuel gauge (Passenger side - terminal) -----> Tan wire -----> Tank sender -----> Rheostat (0-90Ω) -----> Ground.

The sender should read 0 - 0.6Ω at E, 44.9-45.1Ω at ½, and 88 - 90Ω at F.

That means that when you break the circuit, the gauge should read past F and when you short the tan wire (or the passenger side gauge terminal under the dash) to ground, the gauge should read E.

Some threads about this are located here, here, and here (Search is your friend).

- Eric

 

Ah, yes, the old "hot fuel" issue.

In my limited experience, it is usually the tank ground to frame, sender to trunk connector wire, or the pins/ terminals at the dash pod.

 

Thanks for the quick reply, I forwarded to my son, This car is all original and has been sitting up for years so I know it will have a lot of bugs to work out,

I recently turned it over to my son so hopefully together we can keep it on the road.

 

For me it was the fuel tank sender unit. I double checked everything else. Replaced sender problem went away.