Fuel gauge works only most of the time

[WolfRichter]

Dear R4 people,
I hope you`re doing well. My fuel gauge on my `85 850cc R4 kind of decides spontaneously if it`s going to come to work on any given day. Sometimes it just quits mid drive, only to twitch and come back on later. I asssume a bad connection and since i`ve had the dash apart i suspect on the gas tank side, however before i go and tear that thing out i wanted to check with you if there`s something i might have missed or a trick i could try beforehand.
Thanks in advance.

 

[André4Renaults]

The first thing to do is to gain access to the top of the sender unit.
1/Remove the live feed to the float unit and connect it to a good earth. With the ignition on the petrol gauge should now read "full" and remain so. Leave this connection in place and drive around for a day or so and see if the gauge moves. If it doesn't, the fault lies elsewhere. Re-connect the live feed to the float unit.
2/Somewhere between the tank body and the car frame there's a wire that earths the tank. I can't recall precisely where this is, but a good hunt around under the car, with the aid of a torch should prove beneficial in finding it! When you find it, ensure it's in good order and that both ends are clean and shiny, ensuring a good electrical connection. If you can't find this wire it might be worth looking for a male spade terminal on the tank and use this to earth the tank.
I hope this helps! An intermittent gauge suggests a lose or damaged electrical connection somewhere.

 

[Andy McGhee]

This problem can also be caused by a poor connection in the fusebox - try pinching the contacts that hold the fuse to see if there's a difference.
I remember you said you'd had a problem with dirty/corroded fuse connections before. Anyway, it's a good place to start!