Classic/Antique Car Repair: Fuel gauge, chevy c10, fuel gauge

Question
Hi i have a 81 Chevy c10 and the fuel gauge isn't working it is pegged at full. I've messed with the wires on the gas tank and it seems that when you hit a certain way it makes the gauge bounce around but does not stop at a certain point. I am lost on what it could be.

Answer
It sounds like the tank sender unit might be bad. To check it disconnect the fuel gauge wire at the tank and turn on the key. The dash gauge should drop to empty. If it does not then there is a short in the wire to the tank unit or the dash gauge is defective.