Martin's928

Hi all, new to forum, 1988 S4 5 spd
Recently began having electric problems. First noticed headlights working erratically (not raising/lowering consistently and not lighting consistently). Soon after this HVAC blower started cutting out with brake pedal press, now not working at all. I have traced all the X-bus supplied functions and these are what are giving me trouble. Brake lights only on when side lights on, HVAC dead, headlights as noted, no fog lights, no wipers, no central lock. Not sure about cruise control. Unsure how to check evaporator thermal switch but this is on x-bus. My power windows are fine though and they are x-bus. I also have no four way flashers and signal lights but I'm wondering if these are not working due to the brake light issue.
Anyway, I've cleaned all grounds, replaced or am replacing relays, checked/cleaned all fuses and cleaned all plug contacts, taken central elec out and traced x-bus and found no problem, installed new ignition switch, sequentially removed and replaced central plugs and relays to try and trace problem with no clues.
Any help would be greatly appreciated.

Tampa 928s

If you want to spend the time and learn the electrical system read this. Allan Moore's guide! http://jenniskens.livedsl.nl/Technic...WDP%20Only.pdf

This might help
https://rennlist.com/forums/928-foru...f-grounds.html

linderpat

Wow; you've covered everything there is to start with. Sounds like you still need to replace a couple of relays. Did you follow the ground point diagram and make sure you got all of the grounds, including the ones in the back near the battery?

Martin's928

Thanks for the links Tampa 928s, had one but not the other.

linderpat: thought I'd cleaned all the grounds but you said 'ones" in back near battery. I got the main ground strap behind the tool kit cover but, when I re-checked the diagrams, missed the one under the spare wheel! I'll get that one done. Let you know if it helps.

Alan

You probably need a new ignition switch (the electrical part only).

Verify your X-bus functionality at the top of any of fuses 1-5 (for an '88) Test for voltage in the dimple of the top fuse blade. Wiggle the ignition switch in accessory or ignition mode - if X-bus is not present or is intermittent replace the ignition switch. Get a quality Porsche or OEM unit (Rog100, 928intl etc)

Alan

Martin's928

Alan: as noted in post, ignition switch replaced. Traced many of the circuits last night and will be pulling the fuses you mention and looking for voltage. Also plan to jump relay IV to make sure my HVAC works and isn't the problem. I'm hoping that with those fuses pulled one at a time, I may at least start isolating the problem a little. I think I'm getting closer but just can't seem to nail the issue.

Alan

Where did you get the ignition switch from? Not all are created equal...

In any case do the same tests to check the X-Bus. You don't need to pull the fuses... all the tops of those fuses are connected together to X.
BTW this issue probably isn't a grounding problem - unless you have multiple ground issues.

Alan

Martin's928

Thanks Alan. It's a Kostal switch from Pelican and listed as OEM. When I installed it, it appeared identical to the original. Made no difference to the problem though. At the time I thought it might work but might not help. Now I'm disappointed as it appears a very likely culprit. The original switch I was getting a little flickering of the gauges (speedo?….can't remember) if I moved the key around. It's rock solid with the new switch though and seems to be working properly.
Good to know it's not likely grounding as I did feel I'd exhausted that trail a while ago. I will clean the ground point I missed but I'm not optimistic it will make any difference.
Any other thoughts out there?

Alan

Do test the X-Bus levels as I noted - you need to know if X makes it reliably to the CE panel.

Alan