Zshark

1985 928s Euro Auto

I noticed this problem after I disabled my car alarm. If you follow the thread below, you'll see that I incorrectly jumpered the system which resulted in a short circuit that damaged some wiring in the car.

https://rennlist.com/forums/928-foru...ot-disarm.html

Now my tail lights are acting crazy. Look at my video please. You'll see the problem arrises when the headlights are on and the turn signals are on. The problem gets worse with the brake lights on, the turn signal on and the head lights on. Its hard to see in the video, but even the reverse lights come on with the same frequency as the turn signals, this is while car is not in reverse. My current theory is that I fried the check bulb module when the short circuit event happened. Any other thoughts as to what could cause this? I have checked the main circuit/fuse panel, unbolting it and checking front and back. One black/red striped wire (Im assuming same one that goes to the alarm module) was burnt and the insulation was damaged. I repaired that wire and checked the surrounding wires and the connector for it, I didn't find any further visual evidence of damage to the main board. I am trying to think of where the different lights could be forming a circuit, and the check bulb module is a place where all the light circuits converge. I have already checked and cleaned the ground point inside of right quarter panel near rear of the car.

Mrmerlin

you should disconnect the battery then drop the Ce panel and examine the wires on the back looking for any wires that have a satin finish to them, these will be wires that got hot.
Look for where these gray wires have melted to crossing wires and to where they plug into the back of the panel and connect to the front and to the wire run to the lamps.
You will need to trance them from the POD switches to the turn signal switch to the CE panel to the lamps.

Pay close attention to the connectors that go to the rear lights also trace the harness to the tail lamps it runs along the floor and then up the b pillar to the lamps on the right side.
In essence you will be looking for wires that have melted together .

NOTE dont connect the battery till you have found the point where wires have melted together or you might smoke the rest of your harness and CE panel.

Zshark

I've started tracing and have already found more damage. it seems that the wire got hottest near connectors and not as hot in the main length of the wire. hopefully ill have good results soon.

Zshark

So if the reverse lights and marker lamps are blinking on the frequency of the turn signals, does that mean my short circuit is occuring down stream of the turn signal relay? Or could the short even be before the relay? Seems to me that it would have to be down stream of the relay.

Christopher Zach

Hm. How did mis-jumpering the alarm blow up your wires so badly? They should have been fused lines, so unless you sourced a 30a fuse to a 5a line I'm wondering why it went to smoke?

(Note: My driver's side heated mirror shorted and did some annoying melting of the in-door wiring harness. So glad the harness blew up to save the 10 cent fuse in the panel.... More to the point, they used thinner wires in the door than what the fuse is rated for. Bad Porsche, bad ampacity!)

Zshark

Could be wrong, but maybe the alarm system doesn't have a fuse, because thieves could learn how to pull the right fuse and disable the alarm. Looking at the wiring diagram, I don't see a fuse, or I don't know how to properly read it.

Alan

Its a grounding problem at the rear lights - check the ground connections.

Alan

Zshark

So Ive achieved some progress. Ive repaired all of the wires in the loom near the main battery ground wire point. They had been modified, probably when the car was federalized. I have undone those modifications and soldered the wires back and have insulated some wires that were damaged during the federalization process. Please see above pic and tell me if this is another modification to the rear wiring harness. This doesn't look like Porsche work to me, but I just want to confirm. With the progress Ive already made, the turn signal issue is less severe, but the left marker lamp and brake lamp kind of just dim now when the turn signal is on. The reverse lights seem to be no longer affected. I think that this tail light issue may have nothing to do with the alarm system problems I had earlier. But all this stuff happened at once so its hard to tease out what is causing what. Thanks for everyone's help.

Alan

Temporarily add a new ground between the ground point for the battery and each of the rear light cluster grounds - I think you will find it solves these problems. Then find where the grounds are actually compromised and fix that.

It could be damaged wires - it could be corroded connectors...

Alan