Michael Benno

Hi gang:

I could use some help trouble shooting an electrical problem that arose after a replacement stereo installation. My car is 1988 928 S4 5spd. LHD.

Problem description: The central warning indicator is glowing dimly when it should normally be off. The bulb will fully illuminate when it is supposed to: Parking Brake, Test while starting, etc).

Problem analysis: I am going to assume this light is activated by the controller completing a ground circuit for the various conditions, correct? If so the dim illumination must be some sort of partial ground through something that has some resistance (e.g. the controller?). Does that sound correct?

This problem arose as a result of a stereo installation that i paid for. The simple answer is just bring it back to them and have them fix it. I did once already. They didn't find it but they promised to take it in again and research. They are not 928 experts and I don't particularly want them digging around in my car anymore. I'd rather take it to a 928 Guru or solve it myself at this point.

Possible causes: I think the issue is a result of a significant short circuit. I do know that the tech accidentally grounded out the trunk release on the passenger side. This apparently blew some fuses and the bulb for the fog light and headlight switches, and likely killed a cell in the battery as that needed to be replaced too (which they did). Do you think a short circuit caused this? Which system do you think are affected the warning controller? It seems to be functioning normally.

I am fairly certain the problem is not a result of the new radio wiring. The new system receives fused power directly from the battery and grounds to the OEM locations for both the amp and head unit. All speakers are using new wires as well. The head unit receives the "ignition on" signal from a splice into a switched power wire in the console area (can't remember witch one right now).

I realize electrical gremlins are tough to chase down. But I could use some help in sleuthing. Should I start with unplugging the warning control module to see if the bulb stays illuminated? I do have a multimeter and have a rudimentary understanding of how to use it to test connectivity and resistance. Your constructive thoughts appreciated in advance. Thank you.




This is a sample pic so you know which light I am talking about. This light is showing the fully illuminated state, not my dimly lit state when inactive.

Michael Benno

Problem solved - turned out to be a blown fuse at #7: keyboard lights, light switch light, diagnostic connector.