89 Porshe 928 Dash lights Not Working When Headlights Are On

[Raffaele Sottil]

I purchased a 89 928 2 Years ago and have had very little time with her. This was not a car I was looking to purchase, it just showed up in the local ads so I decided to take a look as I’ve always liked these cars, the shape is timeless. The car looked good but I knew it would need work as it was sitting under a tarp for 3 years. If I didn’t but it, it would go to scrap for sure. I couldn’t let that happen. So far, I’ve put in a new transmission, rotors, callipers, gas tank, torque tube, various sensors and modules. (don’t ask at what price).

The interior was and still is a 9/10. The issue I have is the dash lights, at first they would flicker on and off as I drove. After tinkering with it, I figured it was the rheostat located under the dash left hand side. I bypassed the rheostat and connected the wires so it worked great. No when I turn the headlights on the dash lights go off. The dash lights only work when the headlights are in the off position.

Does anyone have any suggestions? Could it be the headlight switch itself? How can I test for that? Also, What interior lights should the 928 have at night?

[dtool242]

Put in a new dimmer switch instead of just jumpering it and see if that fixes your problem

[Alan in AZ]

What you described actually doesn't make much sense - I'm not sure it works as you describe - please be precise for a good diagnosis.

The dashboard (pod) lights should always be on with the ignition on. Without the lights on they should be at a brightness independent of the rheostat (also independent of the rheostat even existing). For digi-dash cars they actually do vary brightness dependent on ambient light only (sensor at the top in the middle).


When the lights are on this mode is disabled and the supply for illumination comes from the variable rheostat supply - this also supplies the console lighting at this time (HVAC illumination, ash tray, clock). Obviously in this mode the rheostat is required to be functional and an alternative (max brightness) is a jumper in its place.

Each pod switch should be illuminated brightly when activated, the light switch is always illuminated with ignition on, fog, reset, hazzard and rear defrost should all light up dimly with lights on.

Alan