The_Remora

Maybe some of you electrical gurus can give me some advice in troubleshooting the various electrical gremlins that I'm chasing around in my '87 S4. Sorry if the post is a bit long and disorderly, but I've got to start somewhere.

Basic history of the car is that it had a 5-speed conversion done sometime in the past, several PO’s ago (which could be the reason for some electrical oddities) and other than that, there really is no existing history; I got the car w/o service records or option codes and with some of the interior disassembled where there was obvious electrical problems that were ongoing but not resolved. I've ignored them thus far because the car drives fine and the glitches seem to only affect non-critical items, but now I'm getting serious about fixing them.

I recently replaced all of the fuses and found that several were blown or the wrong rating for the application. This brought various interior features back to life. The interior lights began working again, but I figure the fuse will blow again unless I can find the short. I have to keep the light switches in the middle position off setting in between ‘always on’ and ‘off after doors close’ settings because otherwise they stay on. I plan to switch to LEDs soon so that they won’t draw much in case they inadvertently stay on.

So now I’m looking for the short. I checked the wiring when I replaced some dome bulbs and the ones I’ve seen were in order. I know that any interior light Brown/White wire swapped with the brown wire or shorted to any exposed metal/ground point will circumvent the dimming feature and cause interior lights to stay on.

There are several severed wires around Ground Point ‘MP IV’ that you can see in the below grainy camera phone photo. These wires have just been laying there like this... Note, after I took the photo I taped up all the ends with electrical tape. I'll go back and see which have power to them and try to correlate them with controls and features this weekend when I get back into it. There is also another severed wire that is not in this picture that I just discovered later today after I had taken this photo. It is also in the rear but on the gas tank side of the car.

The green severed wire-1 looks like it feel out of the adjacent plug, but the wires out of the plug are brown and brown/white. I couldn't find that combo in the wiring diagram. The other wires look like they might have been accessories, particularly severed wire 3 just looks like speaker wire. Possibly wires 2 & 4 were grounds, but aren't grounds brown in these cars, with brown/white grounding to relays? I couldn't find too many black wires in the diagram that looked like they would live in this vicinity...

I’ve been looking at the factor wiring diagrams to see what systems ground to MP IV.
The ‘interior lamp contact switch’, ‘interior lamp roof’ and ‘interior lamp trunk lid-2’ all ground here. It also appears that the speedometer impulse sensor grounds to MP IV. Since the speedometer/odo is still not working, this would be the next logical place to fix in troubleshooting this. I will be able to get under the rear of the car soon to verify that the pick-up is still attached properly. If these don’t fix the speedo then I’ll tear into the dash pod as soon as I have time.

The only other feature that appears to use this ground point MP IV is the Rear Wiper motor and relay. The rear wiper hasn't functioned since I've had the car. I may just take 'delete' it to save weight and clean things up since I never used that on my other 928 anyway.

You can see in this picture of the fuse/relay panel taken right after I replaced all the fuses that two relays are missing and are jumpered; the XIV Starter Relay and the XXII Reverse Light Relay, which is called the Reverse Light Bridge for 5-speeds, so maybe it is supposed to be like this now?

Does the having power always on to the Starter circuit cause any problems w/o the relay switch in place? Is it possible that this was done because the circuit was different for the manual transmission and the stock relay was for an automatic?

Speaking of automatics, my dash auto-trans gear indicator lights come on since I replaced the fuses, and since the car is now manual this is annoying. Any idea which fuse controls this? I have gone back through the fuse diagram/labels and there is no clear indication of which fuse controls these lights and whether that fuse is also used to power anything else. I could go through and pull fuses until the light goes off, but w/o testing the other controls, some of which are still not working, I won’t know if I am taking power away from another function as well. I would eventually like to remove the bulbs, or better yet to swap the tach face plate for a manual one. Anyone have a suggestion on the best way to deal with this?

Thanks for advice on any of these matters
Chris

Alan

Why assume this - I wouldn't... sounds like the interior lights work but stay on in switched mode - focus onfixing that... It may well be swapped wires between Brown & Brown/White - remove all 3 roof/hatch fixtures - disconnect all wires and start again. Red to the bulb connection, brown to the frame connection, brown/white to the switch connection. BTW here is no dimmer - only an off delay (relay). Once you have checked the fittings if its still gives issues remove the rear hatch switch connection in below the hatch lock receiver, if it still gives issues remove the delay relay?

don't change anything until you figure out the problem - it just makes it harder to debug..
yes mostly looks like aftermarket - trace it back the other way and plan to likely rip it out... yes 928 grounds are pretty much always brown...
It may be that - on a MT car there are 2 more connections on that plug (its a 4 pin not a 2 pin) for the reverse switch - AT's had the relay direct to the bulbs. MT should go from the bridge to the transmission (mounted) switch through this point and then to the reverse lights - some of those extra wires may be for that... do your reverse lights work? The pulse sender connections should be Red/White on the car side of the plug... I don't see green...
Remove the starter realy bridge and replace with a stadard SPST relay ('53 type) - do this right away before you destroy your ignition switch neither AT nor MT should be wired like this. The reverse relay is jumpered in an MT - this is correct. Black sticky tape on the pod glass to start with (temp only) then yank the bulbs when you get into the pod - its easy - there isn't a seperate fuse just for this.

Alan

Mrmerlin

as always disconnect the battery when working on the elex system

The_Remora

Awesome advice, thanks guy!

Oh, and yes the reverse lights do work fine.
I checked to make sure the brown and brown&white wires weren't crossed on some of the interior lights but not all, I will go back through more thoroughly.
BTW, I meant to type 'MP VI' and noticed I'd been typing MP IV, a differnt ground point... damn dyslexia