It's pretty easy to break the problem into two pieces. If the gauge is properly powered on one side, and the other side goes to the sending unit, then turn the key ON, pull the sending unit wire (at the sending unit) and the gauge should read FULL. Same deal but ground that wire. Gauge should read EMPTY. If all this works, the gauge and wires are fine and the problem is the sending unit or its connection with ground.
I think this is how it works!
Stuart
