A fuel gauge that pegs to EMPTY when the key is turned on means there is a direct, or GOOD path to ground. If you did Wrenchbenders test at the tank, and the gauge reacted as he described, then the gauge AND wire clear back to where you are checking is fine.
If you have the key on and touch the wire to the proper post on the sending unit and the dash gauge pegs on EMPTY, either the tank is empty, the float has sunk or the sending unit is defective.
A insulated tank or any poor ground between bed, tank or cab would result in a FULL gauge reading.
It looks like the next step would be to pull the float/sender and take a peek.
This is how it looks to me.
Stuart
