Two electrical issues

[wenbeaver89]

Ok so i have two issues right now! First the car, I have a 87 325is with a m50 turbo swap.
First problem: My gas gauge dont work! I tried switching clusters and fuel gauge sending unit thing with other ones i had and neither made a difference. Not sure exactly how to test this?

Also the windows/sunroof etc. They all work fine but intermittently they will not work. Everything just freezes up and after awhile it will start working again??? Could this be a relay or something?

[SmokeE30]

The window issue could be the circuit breaker. Is there a particular time they stop working like closing the window for example?

[Gregs///M]

Gas gauge is directly wired to the gas tank senders. If you've swap both with no success then the wiring could be a possibility. Inspect the local wires at each harness connector for corrosion, pins that have been pulled out, or damaged insulation on the wires itself.

Get the ETM manual for your car and test the senders from the tank up to the front the car to figure out where the fault is.

For your windows, it could be the circuit breaker. But also check the window switch grounds above the brake pedal on the two 10mm nuts near the steering column. You will see a bunch of brown wires leading to those nuts, clean the ring lugs and re-secure.