These gauges won't have fuses in the fuse box.
Check the wire and clip on the sender at the front of the block (make sure its not broken/corroded/fallen off/loose etc)
Check all the wires on the sender. Sometimes they can break off. Or being old, the terminals on the plug can get corroded etc. GOOD clean up if req'd.
Last time mine stuck on half, one of the 3 wires broke right at the sender. Geee, I'm getting good fuel economy this week!.....As I ran out of fuel in the middle of knowhere
Possible faulty sender in tank?
Do you have access to a multimeter to check for voltage and resistance/continuity (for broken wires) in the wiring?