GMM928

Hi all,

I've managed to screw up my interior courtesy lights (no longer functioning), and I can't figure out what went wrong...

Over Thanksgiving, I decided to remove a crappy, old Audiovox alarm unit installed by the original owner. I was pretty careful in tracing and removing the alarm wiring (all located near/around the fuse/relay board), but when I re-connected the car battery my interior lights would no longer turn on when I enter the car. All of the interior lights still work when switched to manual mode, and I've checked all of the fuses that I thought could be the problem. All seem fine (including fuse #25). My central locking function still works fine as well. I have tested the two front door pins (not the rear hatch pin), and the relay under my passenger seats clicks when the doors opens (theoretically to turn interior lights on) and clicks again after several second when the door is closed (theoretically to turn the interior lights off). So, my guess is the relay is still good.(?)

I read most of the threads I could find on this topic, and then sent a PM to Alan in AZ as he seems to be the resident expert. He was very good about sending me the following PM (thanks, Alan):

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Your model year has a combined interior light/alarm and central locking module under the passenger seat (you must remove it to access).

I suspect inthis case the aftermarket alarm dome light supervision feature was swapped for the factory system. You need to find where and reconnect - most likley is at/near this alarm module - since all the wires required for an aftermarket system install are located there.

The interior light circuit is the thickest of the Brown/white wires - it will have been intercepted somewhere.
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I went to remove the passenger seat, and found that the bolts holding the seat in place are torqued incredibly high so I didn't manage to get it removed yet. I'm the second owner of the car, and I'm guessing the original owner (as well as the alarm installer) never pulled the seat. Given all the wiring for the alarm was in/around the fuse & relay panel, it just seems really unlikely the seat was removed.

Following Alan's advice, I did find that one of the alarm wires had been connected / clipped to one of 2 brown/white wires in wiring harness P below the relays; my guess is this is where the brown/white wire he mentioned was intercepted. But, I had removed this connection when I pulled the alarm, and the brown/white wire seems to be intact there. Because I didn't pull the seat, I cannot tell if the wire was also intercepted near the relay, but all of the other alarm wiring was in the passenger footwell.

If I'm right that the passenger seat has never been removed (i.e. the wiring there has not been modified), and that the relay is still good, then I'm stuck wondering why the lights work in manual mode, central locking/alarm works, but the lights don't come on in courtesy/auto mode.

Its probably worth noting that my rear interior dome light fixture is in need of replacement. It works fine when switched on, but has always been dim when in auto mode. I'm pretty sure these lights are wired in parallel; it seems unlikely that one bad light fixture could cause my problem.

Worst case, if I have to, I will pull the passenger seat and see if the wiring was modified there (I guess its still possible). Before I do so, it would be great if anyone has additional thoughts on what I can check...

Thanks a lot...

Alan

The seat bolts on my car were loctited (red) - you need to use a high temp heat gun to loosen them - torque won't do it - you will just screw the heads up - hopefully you haven't done that yet. Do raise the seat all the way up front & ear and use the best quality allen head sockets you can find - after thorough heating.

I think you have to see what is going on under the seat.

Alan

GMM928

That makes sense, Alan. I have not yet screwed up the bolts. I've used a small torch for unlocking wheel bolts. Not sure yet how I'm going to get enough heat onto the bolts, maybe just a heat gun with some shielding?

NC928S4

Could have accidentally disturbed or disconnected the leads that are connected to the rear hatch release when you disconnected the battery?

borland

If you had the WSM wiring diagrams, you could trace the BN/WT special ground (e.g. 'auto') wires where they enter the CE (fuse/relay) panel at connector plugs U and P. Inside the CE panel, those wires connect to the light timer relay.

I wouldn't use heat on those bolts. You only need the correct size wrench with enough leverage to work them loose.

Alan

A '91 doesn't have a timer relay on the CE - its in a module under the pass seat...

On late model cars Porsche loctited these bolts - if they are loctited - you won't get anywhere... trust me - BTDT...

This seems not to be true of earlier cars - may be related to direct seat attach belts.

Alan

Alan

The rear hatch pin switch can cause them to be on when they shouldn't be... but not to be off when they shouldn't be...

Alan

borland

Alan, Your right on the location of the timer, but the '91+ also uses CE panel plugs U and P for the BN/WT special ground wire.

GMM928

Borland, thanks for your comments. I've got the service manuals, but for some reason my Volume 6 only goes up to 97-011, and I think the wiring info I need is located in 97-367. So it must be in Volume 7 (which of course I do not have yet...) Have to track that down. I didn't notice a BN/WT in plug U, only P. Will check that again.

I'm going to try to get the seat out this weekend or early next week and see what's going on under there (and will use heat to break the loctite - I already tried using a huge amount of torque and that didn't work). Its seems logical that the BN/WT was cut or intercepted there (or somewhere), then routed back into the panel via the alarm system that's no longer present....

Takes no time to check the rear connections as well, so although Alan is probably right I will check those as well and report back.

Thanks very much.

borland

The wiring diagram for your '91 shows four BN/WT (Brown/White Stripe) wires terminating at Plug P. One of those wires at Plug P runs to the Factory Alarm Control Unit's pin 7.

- Check continunity between Pin 7 of the Factory Alarm Control Unit and Plug P.
- Check continunity between Plug P and Plug U.
- Check continunity between Plug P and interior door & CE panel lamp sockets.
- Check continunity between Plug U and interior overhead & tailgate lamp sockets.

GMM928

Thanks borland, will do.

GMM928

Accessed the Factory Alarm Control Unit under the passenger seat (doable from behind the passenger seat without removal).

No modifications to the wiring found at the module. I checked continuity of the wiring with my multimeter: all connections are good:

Have continuity between Pin 7 of the Factory Alarm Control Unit and Plug P
Have continuity between Plug P and Plug U
Have continuity between Plug P and Interior door light's switched ground wire (BR/WT)
(did not check the CE panel lamp)
Have continuity between Plug U and overhead light (did not rear dome or rear hatch light).

So does this mean the alarm/locking/interior courtesy light relay is not correctly switching to ground (despite making all of the right noises, and all other functions working correctly)? Is there a simple way to test the switched ground that's supposed to be coming from Pin 7 in the alarm control unit? Sorry, probably a dumb question; it seems I now know the connections from the relay to the lamps are good, and that the lights all have power, so it must be a relay problem given they don't turn on...

Bummer if I need to replace that unit; I think I read in another post that the part in not cheap...

borland

First check the door pin switches to make sure they are sending the low potential signal to the Alarm Controller. The door pin switches connect the special ground to chassis ground.

Check the door pins function at pin 21 of the Alarm Controller (BR/WT). Check the tailgate switch function at pin 3 (BR/WT) of the Alarm Controller.

You can simulate the interior lights turning on by pulling the BR/WT wire to chassis ground on the Pin 7 side of the alarm controller (At pin 7 or at Plugs P or U, you make the call). This bypasses the Alarm Controller.

GMM928

Thanks, borland.

Seems odd that all 3 switches could go bad at once (all were working before). And, all pins cause the controller to click, so I think they are sending the low potential signal (or do I need to actually check at pins 21 and 3?).

I will simulate the ground from pin 7 on the controller and let you know how that goes...

borland

If you check the door/hatches, that would determine if the Alarm controller is working. Simulating the ground at pin 7 would rule out any problems with the wires leading to the lamps.

The tailgate motor release mechanism also uses the same special ground to the door pins. If still wired per the factory wiring, the hatch release switch by the driver seat requires the door to be open in order for the motor to work. So, if that is working properly, then not much reason to check it.