67-72 Chevy Truck fuel gauge diagnostics 101

[Lancialonnie]

This is a great write up however I am having a slightly different problem. I know my sender works as it is new and tested. My fuel gauge just moves erratically, it goes from being correct to way past full for a few minutes then back to correct and it may stay there or it may go down to empty then back to past full to correct again. There is no rhyme or reason to this, it just moves all over the place. is it a bad ground? Where should I ground the gauge to make sure I have a good ground?

[67 Burb]

Originally Posted by Lancialonnie

This is a great write up however I am having a slightly different problem. I know my sender works as it is new and tested. My fuel gauge just moves erratically, it goes from being correct to way past full for a few minutes then back to correct and it may stay there or it may go down to empty then back to past full to correct again. There is no rhyme or reason to this, it just moves all over the place. is it a bad ground? Where should I ground the gauge to make sure I have a good ground?

How is the sender grounded? It sounds like it momentarily loses ground and the gauge goes past full, then it finds ground and reads correct. If it is using the tank for ground, that may be the problem. It needs a ground wire from the sender to the truck frame.

[Lancialonnie]

I have a good ground on the sender so I believe the problem is a bad ground on the gauge. I'm just not sure how the gauge should be grounded, from one of gauge terminals?

[VetteVet]

Originally Posted by Lancialonnie

I have a good ground on the sender so I believe the problem is a bad ground on the gauge. I'm just not sure how the gauge should be grounded, from one of gauge terminals?

The gauge is grounded to the cluster with the lower terminal on the gauge. If it was bad the gauge would give a non reading rather than what you are seeing. Concentrate on what Burb is saying and check the tan wire connection on the fuse panel marked FUEL. The other possibility is the no. 4 terminal on the cluster plug connection. It is the return path to ground for the gauge.

[TBONE1964]

Originally Posted by Lancialonnie

This is a great write up however I am having a slightly different problem. I know my sender works as it is new and tested. My fuel gauge just moves erratically, it goes from being correct to way past full for a few minutes then back to correct and it may stay there or it may go down to empty then back to past full to correct again. There is no rhyme or reason to this, it just moves all over the place. is it a bad ground? Where should I ground the gauge to make sure I have a good ground?

If you want to add a ground, you can use the center lower terminal on the fuel gauge itself. Do you have any issues with any other gauges/lights? Also check the ground screws on the circuit board, one by the fuel gauge and one by the speedo. The cluster gets its ground through the connector and through the circuit board. very common burn spot on the circuit board is near the connector plug in. Make sure the circuit board does not have any burn spots and the grounds are tight. Also if the cluster tins have been painted, it can cause a ground issue between the fuel gauge tin and the main tin.

Check all the 5/16 nuts on the back and make sure all are tight. It sounds like a loose ground or bad connection to me.

Share what you find here please.

Thank you,
Tom

[Benjamin]

Subscribing

[CarpBlazer]

Originally Posted by TBONE1964

If you want to add a ground, you can use the center lower terminal on the fuel gauge itself. Do you have any issues with any other gauges/lights? Also check the ground screws on the circuit board, one by the fuel gauge and one by the speedo. The cluster gets its ground through the connector and through the circuit board. very common burn spot on the circuit board is near the connector plug in. Make sure the circuit board does not have any burn spots and the grounds are tight. Also if the cluster tins have been painted, it can cause a ground issue between the fuel gauge tin and the main tin.

Check all the 5/16 nuts on the back and make sure all are tight. It sounds like a loose ground or bad connection to me.

Share what you find here please.

Thank you,
Tom

Curious about the common burn spot near the connector on the printed circuit, What could cause that spot to burn out?
Posted via Mobile Device

Edit: reason I ask is that my fuel gauge (71 Blazer) is stuck below empty, I noticed printed Circuit was burned out on ground circuit next to plug in. Replaced circuit and it burnt out again.
Turn signals are also permanently lit..
Grateful for any advice I’m stumped.
Ben

[TBONE1964]

Originally Posted by CarpBlazer

Curious about the common burn spot near the connector on the printed circuit, What could cause that spot to burn out?
Posted via Mobile Device

I am also a bit curious but my thought is it is the closest to the connector but weaker than the wiring in the connector. If any circuit gets shorted to ground, that spot seems to be the weak link in the flow.

While doing my testing, I have fried a few by shorts and that is the spot the burn through.

Maybe some of the others have some ideas. I know it is hard to keep good ones around for long

[CarpBlazer]

Thanks Tom, looks like I’m on the hunt for a short to ground somewhere, I’ll report back once I find out where it is..hoping it will fix this fuel gauge stuck on empty situation.
Ben