If you have the correct electric sending unit for the gauge, pull the original cap tube bulb out of the engine, figure out what thread adapter is needed to install the electric sending unit, one wire from the sending unit to the gauge and wire the hot side of the gauge to be energized with key on. Is everything staying 6 volt?

1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy