Faulty Fuel Guage Diagnosis?

Take the wire off the sender and ground it. With the key turned to run, the gauge should goto full. If not, then the trouble is on the gauge side. If it does, then the trouble is either the jumper strap between the steel fuel line over the rubber hose to the sender (most common failure point) or the sender. Test the sender with a voltage ohm meter. Should get readings somewhere between 85 to 10 ohms or thereabouts.