first check that the 12 volt switched power line actually has power when you turn on key, check the ground at the gauge, make sure it is a good clean ground, then check continuity on sender wire. if not good, replace wire, check ground at tank, also needs to be good clean ground. if you are getting a signal from the sender wire back to gauge and nothing works, and have checked the rest, probably a bad gauge. it is possible to kill one right off the bat if your connections are wrong.