Take the wire from the gauge to the sender on the tank loose and ground it. The gauge should go the empty.
If it does go to empty, the circuit up to the sender (voltage reducer, gauge and wiring) is OK.
If it doesn't go to empty, then the problem is in the voltage reducer, the gauge or the wiring.
Be sure to heed this warning tag when working on the back of the fuel gauge:
Fuel Gauge Warning Tag If your tag is missing, the one in the picture is on the stud behind the FULL side of the gauge.
The voltage reducer should be on the stud behind the EMPTY side.
