Dark Blue

The instrument lights in my '89 S4 all go out when I turn the driving lights or headlights on. They are all on when the lights are not on. I think it's related to the left under-dash dimming wheel (potentiometer?). I used to be able to play with the wheel and they'd come back on, but now nothing. Is there a good way to clean/RR that dimming wheel and/or replace it. Thanks!

Steve
89 S4 Auto

Ed Scherer

It probably is.

See an old post on this topic and follow the links in that post for yet more tips.

davek9

As a quick test to see if the POT is bad, pull the two Fast-on connections and place a jumper in place of the POT.
You should get Full Brightness on the lights.

Dave K

Bucko74

Whilst I'm not 100% sure, but I think there are two circuits that run the instrument lights. one is active when you dont have you headlights on, the other goes through the potentiometer when headlight circuit is active.

MY simple diagnosis would be the POT needs refurb or replacing if you get instr lights without headlights and no instr lights with headlight on.

I know when my instr light went, the potentiometer was the culprit (as with most posts on this forum with same issue).

OTR18WHEELER

Mine was also bad, so as a safe & easy temporary fix, I used a low amperage blade type fuse as a jumper.