Sounds like you have excessive resistence in the circuit. TAke the wire off the sender, turn the key on, now ground the wire. Tank should read full. Remove the wire from ground, tank should now read empty. ( I may have that backwards, ground might read full, but that is the procedure.) Don't worry about grounding the sending unit wire, the voltage flows thru the dash gauge first, acting as a resistor. If the tank will read completly empty with the wire disconnected, you have a problem in the sending unit. Otherwise the problem is in the dash or wiring. Alt. conversion should not affect it.
