67-72 Chevy Truck fuel gauge diagnostics 101

[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.