Your sending unit and gauge certainly need to be compatibleand the right voltage needs to be applied. The sending unit is nothing more than a variable resistor. The gauge typically has two coils...one that acts as fixed force to deflect the needle and a second coil that is wired to the sending unit. It's the second coil and sender unit that then determine the position of the needle. If the voltage is too high for the gauge, then the fixed coil may dominate how the needle moves. I think some of the older Chilton's manuals describe exactly how a gas gauge works. Hope this helps.