Can someone tell me the proper way a fuel gauge is wired with twin engines? Gauge only registers when port engine is running and always reads 1/4 to 3/8.

gauge has three wires. Ignition which is the power supply, a ground, and a sending wire that goes to the sending unit at the tank. Could have a blue wire also if gauge has a light. Power supply is coming from your port ignition which is the reason it only works with that motor. Probably a bad sending unit

Thanks, would the sending units be a marine version or is there no difference?