If temp gauge is still working, then that rules out the voltage limiter.

If you can disconnect the sender wire from the sender, pull it up into the trunk and ground it with the ignition on. If the gauge begins to climb, that means the wire & gauge are still working.

Double check the ground strap for the sender. IIRC, these are just a metal strip that clips onto the metal fuel line coming out of the tank and clipping onto the line on the frame rail. Often, these rust away.

If that is still in good condition, then the only thing it could be would be the sender itself has pooped the bed. Usually the only repair is to replace.