My fuel gage in my 1996 ford thunderbird don't work?

My ford thunderbird gas gage is all the way past full and does not move any susgetions on how i can fix the gas gage

Disconnect the wire from the tank sending unit (at the tank) and see if the gauge goes to zero. If it does replace the sending unit. If it still reads full remove the sending unit wire at the gauge terminal. If it then drops to zero the wire is shorted to ground. If it instead still reads full the gauge is bad.