First thing I would check is to see if there is a good ground from the fuel tank sending unit to the frame. If there is not a good ground the gauge will not read properly. This is a common problem. If you are certain that the sending unit is bad try Clark's Corvair Parts at www.corvair.com. Page 69 of their catalog I think is where you will find it.
Most times the fuel gauge sending unit in the fuel tank is at fault. And once again, most times it requires removing the fuel tank to gain access to the sending unit for replacement.
Fuel gauge problems are usually the fault of the fuel gauge sending unit in the fuel tank, just saying.
Assuming you mean the fuel gauge sending unit, the fuel gauge sending unit is part of the fuel pump module and not sold or serviced seperatly. The fuel tank must be removed to access the fuel pump module for replacement.
It has several sending units such as a fuel gauge sending unit, oil pressure gauge sending unit, temperature gauge sending unit, need to know which one you are looking for.
In most cases it is the sending unit located in the fuel tank that is at fault. Replacement is necessary.
Replace with either a manual gauge or just a similar replacement part.
Bad sending unit, corroded wire from the sending unit to the gauge, faulty fuel gauge are a few.
If the gauge isn't working, then the sending unit has failed.Easy enough replacement and doesn't cost much.See "Related Questions" below for more
If you are have fuel gauge problems I would suspect the sending unit in the fuel tank to be at fault. Rarely the gauge is the problem.
Most fuel gauge problems are caused by a faulty fuel gauge sending unit. The fuel gauge sending unit is located inside the fuel tank. In most cases the fuel tank must be removed to replace the sending unit.
Check for power and ground to the sending unit . If you have that then ground the sending unit and see if it works.If the gauge works then the sending unit is defective.
Its normally the sender. Take the wire off the sender (on the tank) and earth it. Turn the ignition on. If the guage rises the sender needs replacement. If not then its more likely to be a wiring fault than the gauge itself