[AzDon]

Using Zac's advice, with the tank full, try running a dedicated ground wire from one of the tank-sender flange screws to the chassis. If it doesnt now show full, try pulling the hot wire off the sender and grounding it directly to your new ground wire. If it now shows full, the sender is no good. Look at the gauge with the wire disconnected: Is it now showing empty rather than 1/4? This is further verification that the wire to the rear and gauge are working, but the sender isnt!