Shmoo,
It sounds like you are pointing the guilty finger at the sending unit. Here is the nickle tour for the whole enchilada.
Key ON, pull wire from sending unit at tank, gauge should read FULL.
Key ON, ground that same wire to a known good ground, gauge should read EMPTY.
The drill tells you that the gauge works, and the wire from gauge to tank is contiguous.
The gauge needs 6 volts, and should be grounded in the cluster assembly according to Hoyle.
If all this happens properly, the culprit is the sending unit, or a poor ground to the sending unit.
Stuart
