Gas gauge has spun past full and appears stuck

the fuel sending unit in the tank is a rheostat wrapped wire it increases the resistance read at the gauge the more fuel the more resistance.
what it sounds like is a dead short either in the sending unit or the wire running to it.
to check sending unit in the tank, locate the closest wiring harness plug (in the trunk/or under car) and disconnect then check gauge reading,remember ignition must be on.
try that and get back to me if needed