To check the guage: disconnect the sender wire at the tank and ground it. Turn the key on, the guage should read empty (if it does, your guage and wiring are good and the problem is either a bad or stuck sender or a bad sender ground). If it still reads full, (sender wire grounded), the sender wire is open or has a bad connection at the guage, guage not grounded to housing, or the guage is bad.
