I just restored my car (1970 Datsun) and the only thing I can't get to work is the fuel gauge. I have a brand new gauge (just a fancy and expensive ohm meter really) that is correctly programmed. A brand new sending unit (giving the correct readings when not installed in the car) and I recently just replaced the wiring which I previously blamed for running out of gas numerous times.
It's an old car which means metal gas tank that is grounded. The sending unit has two pins (one of which is connected to gnd via tank) and the other one is the sensing pin for the gauge. I am running both pins right up to the gauge in a shielded wire (floating at the sending unit and connected to GND at the gauge).
The car is properly grounded and I also tested it by running another wire from the - terminal of the battery directly to the GND pin at the sending unit.
However, I seem to be running into some kind of ground loop issue as I get wrong readings and electrical load on the car (e.g. turning on headlights) affect the gauge.
I drew simple schematics on how everything is wired.
Measuring the pins directly with an ohmmeter (not powered from the car's battery) gives me the correct readings.
Thank you very much
Kind Regards Michael