john820

928 S4 1989 auto problem with the dash lights with the engine running all dash lights are on and good, when we switch the side/headlights on all the dash lights go out !!! the only thing that is still showing (mileage)
We have had problems with electrics and cleaned all earth points and taken all fuses out and cleaned everyone all electrics working good, can anybody point us in the right direction or had this before.

soontobered84

There is a rheostat under the pod on the left side. ( a wheel-like thing) Your dash lights come on when you start the car. When you turn on the headlights etc, the lights will dim to whatever the rheostat is set to. Just roll the wheel on the rheostat to adjust the brightness/dimness of the dash lights

robot808

john820, This is absolutely the place to start. Your problem may be (and I hope is) that simple. This is a great illustration of how important an owner's manual can be. If you don't have one, it is well worth finding. All kinds of things in there that it might take forever to figure out on your own. Most cars these days you can get in and know exactly what everything does. I don't think it is true of sharks.
Good luck,

john820

thank you did know about the thumb wheel but not working when bought car and lights on dash worked ok looked at the manual before but looks like the rheostat needs replacing???.

robot808

john, I am sure you can you can jump the rheostat to check. That would just take a second.

soontobered84

John,
pull the wires on the rheostat/dimmer and connect them together (jumper them). Try your lights. They should come on full bright. No down side to doing it this way really, you just won't be able to dim your dash lights should you desire to., and it's not factory spec.

john820

thank you did what you suggested and lights working on dash OK but without dimmer will replace the rheostat have you ever changed one ??? been reading the manual and veiwing the problems of the dash not showing the mileage very well and you need to clean contacts mine are a little dim. much of a deal to get the dash out???

robot808

its kind of a pain, but not really that bad. I have done it so many times its gotten quite easy. one thing is to mark the plugs as to how they match up with their respective pod switches. makes putting it back together a little easier. I used a sharpie.

aaron3

I had the same problem. The backlight on the dash works when the headlights are OFF, but when you turn the highlights ON, the backlight goes off. There is a wire connection that gets loose (and sometimes has come off). The connection is above the brake or clutch pedal (can't remember). You basically need to stand on your head to get at it. I think the connection is on the firewall, again I can't quite remember for sure, but I do know you need to lay on your back under the pedals to see/access it.

This happens at least once per year on my 90 GT. One of these days I'm going to put a permanent solder or something on this connection.

My issue had nothing to do with my rheostat. Good luck.

Mrmerlin

to replace the rheostat unscrew the single screw about 3 turns leave it in place then pull rheo out a bit till it disengages from its pin once you have it our you inspect it plug the wires in B4 you install the new one