Fuel gauge diagnostics

[1972RedNeck]

1963 Chevy. Regulator died and over volted the temp and fuel gauge. Got the charging problem fixed. Bought a temp and fuel gauge from Truck and Car shop. Temp gauge works perfect.

Fuel gauge does not work. I have 12 volts at the gauge. To bypass the whoe sending circuit, I grounded the sense terminal at the gauge. Gauge should go to full when grounded but it just sits below empty and doesn't even wiggle.

They sent me another gauge to try - same thing. Again verified power. Again grounded sense terminal at the gauge. Still does nothing.

What am I doing wrong?

[ray_mcavoy]

Grounding the sense terminal on the gauge should cause it to read empty (like you're seeing), not full.

For additional testing purposes, connecting the gauge sense terminal to through a 15 Ohm resistor to ground should cause it to read half. Connecting it through a 30 Ohm resistor to ground should cause it to read full. And leaving the sense terminal disconnected should cause the gauge to peg beyond full.

[1972RedNeck]

Originally Posted by ray_mcavoy

Grounding the sense terminal on the gauge should cause it to read empty (like you're seeing), not full.

For additional testing purposes, connecting the gauge sense terminal to through a 15 Ohm resistor to ground should cause it to read half. Connecting it through a 30 Ohm resistor to ground should cause it to read full. And leaving the sense terminal disconnected should cause the gauge to peg beyond full.

Hmm, this one stays way below empty no matter what…

[ray_mcavoy]

So no needle movement at all regardless of what you do with the sense terminal, correct?

That might be due to a bad ground at the gauge.

It's been a while since I've had one apart, but if I remember correctly, there is a ground contact on the back of the gauge that has to make electrical contact with the cluster housing. So check that area of the housing to make sure it doesn't have any surface rust, paint, etc. that would prevent a good contact. Might also be worth checking the gauge itself (compare it to your old one if you still have it) to see if maybe the new one is made a little different and not allowing it's ground contact to make a good connection with the cluster housing.

[1972RedNeck]

Originally Posted by ray_mcavoy

So no needle movement at all regardless of what you do with the sense terminal, correct?

That might be due to a bad ground at the gauge.

It's been a while since I've had one apart, but if I remember correctly, there is a ground contact on the back of the gauge that has to make electrical contact with the cluster housing. So check that area of the housing to make sure it doesn't have any surface rust, paint, etc. that would prevent a good contact. Might also be worth checking the gauge itself (compare it to your old one if you still have it) to see if maybe the new one is made a little different and not allowing it's ground contact to make a good connection with the cluster housing.

No needle movement no matter what.


I will check this out and scuff it up with a little sand paper. Thanks for the tip...