E30 Zone

The fuel guage on my 1989 325 touring has just started to always register a full tank. I've spotted the advice to sand the earth behind the glove box and also Brians advice to seek out the multiplug connection. Can you tell me where to find this plug on a Touring and what should I look for depending on how the guage reacts when I unplug it?
Cheers

Are you sure it still registers full when you have less than half a tank?

Hi Brian, yes I know it's been pretty low as I filled it with about £50 pounds worth of fuel when it was still showing full.
Cheers

The touring has two level sensors; one in each side of the tank. If one of these sticks in the 'full' position, the gauge will over read, but if there is less than half a tank in total on board, the reading will be less than full, and it's unlikely that both are acting up at the same time.
Under the right hand rear seat cushion, at the extreme RH side, there is a steel tube of about 40mm diameter which contains the tank vent hoses. Cable tied to this tube there is a rectangular multi pin plug and socket. Unplug this connector, switch the ignition on, and see what the gauge does.

Thanks Brian, upon disconnecting the plug the guage reads empty. Could you advise me on the next step?

Thanks in advance!

Mine used to do that. A sharp tap on the cluster above the fuel guage used to send it back to where it should be, which indicated the problem was in the cluster. I removed the cluster and found the earth wire nut on the back of the fuel guage was missing, the temp guage nut was rusty and loose too. I gave them a good clean up, replaced the nuts. Job done!

If it stays at zero with the plug disconnected, then the fault is with the sensors in the tank.
Under the seat cushions and carpet there are two black inspection covers held in place by four screws each. Remove these, pull the two pin connectors off of each as gently as possible, and measure the resistance across each.
They should read between 0 and around 60 ohms each, depending on the fuel level, but I expect you will find that one reads 0 ohms whatever the fuel level.

Thanks chaps, I'll give both options a go. I followed Brians advice about earthing the rear ashtray cable and now my instrument lights are working nicely.

Thanks again