Tail lights warning problem

[concor]

I have a 928s 1984. On my dashboard the red warning 'schlusslicht' shows up, after about 5 seconds when I turn on the lights.
Schlusslicht means something like taillights or so I've been told by a German. Problem is, the two red taillights work just fine! All lights are fine. However, next to the taillight it says 10w6cp. I suppose 10w stands for 10 watt. What 6 cp means, no idea. I've had a 5 watt and a 10 watt in there. Still the warning. I did not check what light bulb the other side has yet. I'm getting out of ideas, help anyone?

[rjm65]

My '79 does the same thing. Tail light warning lights up after a few minutes when the parking lights and/or headlights are turned on. The reset button will turn off the warning, but it comes on after a few minutes. I've cleaned all the ground points (even the one near the right rear tail light) but it's made no difference.

I did check the tail light bulbs, both are the same and match up with what's stamped on the housing. Tail lights work perfectly, and I've actually been standing behind the car with the lights on and have seen the tail light warning come on without even a flicker out of either tail light.... they are on solid.

[surfdog4]

do you know what your alternator is doing when this is happening? On my '81, i was getting the taillamp warning light, but had other electrical issues that prompted me to replace the alternator (actually the regulator was bad but i replaced the whole thing).

Anyway, once i replaced the alternator the tail lamp warning stopped.

Another possibility is bad connections on the instrument cluster...the flexible circuit connectors on there are terrible and all sorts of gauge & warning light gremlins come from that

[concor]

Oh my god. I just disconnected the battery to reset the computer. After that my backup lights don't work anymore. When I put the car in reverse no white lights go on at the back. I checked fuse number 9 for the 'backup lights' which also does the electric mirrors and read window wiper. Both the wiper and the mirrors work, so I assume fuse number 9 is fine too. Well at least the rear lights still work, does anyone have good idea to fix the backup lights?

Hmm, looking at the '84 wire diagram it says 'combination light relay' on relay xix-xx. But the other lights are working properly, so that's probably not it, right? Shall I try disconnecting the battery again and let it disconnected a bit longer?

[Landseer]

The right tail and right rear side marker are on one circuit.
The lefts are on another.

They are the same circuit at the CE panel, but, on their way to the back of the car, that wire runs through a bulb comparator unit, then the signal splits right and left. So two wires then run to the back of the car (along the passenger sillplate).

Bulb comparator is located just to the right/under the passenger tray.

Purpose is to compare the resistance of right side to left side (rear).

Possible for bulb control unit to fail in several ways. First check is bulbs and cleanliness of sockets and connections.

[concor]

Okay, thanks Landseer! That will help with the tail lights warning. The new problem is that after the battery got disconnected the reverse backup lights do not work anymore. Any ideas perhaps?

[Alan in AZ]

The connector from the transmission to the light relay (on an AT) is above the battery box in the spare tire well - did you disturb it somehow... this isthe most likely explantion given what you did.

Its possible you disturbed something in the rear light cluster (but probably not both sides..)

For the bulbs - use fresh bulbs from the same source when replacing - bulbs age and change behaviour (and they are very cheap...).

Alan

[concor]

Hi Alan, yep you were right. It was indeed a loose connector just above the spare tire. The reverse lights are back alive! Actually someone at rennlist hinted me that. But thanks anyway because you were right on track!

Now for the schlusslicht warning. I'll go and replace the other bulb too then. Good idea. And then reset the computer again. Maybe it will be gone by then. Thanks for helping out.

[Alan in AZ]

Ahh - yes I saw that... but you heard it here first (or could have...)

for the bulb warnings - no computer reset / battery disconnect needed (it doesn't work that way)

Alan

[rj7630]

I have a very similar problem with my 84S auto. Everytime I start it up the taillight worning light comes on. If I just tap the brakes it goes off and stays off. Not sure what causes this. The tailights all work just great.

[Landseer]

Yes, I've still got the problem on both of my 84's.

Just materialized on the second one during a bout with alternator failure.

I am very, very close to bypassing the bulb control units on these cars.


RJ, you should get a stoplight warning every time you start-up, that goes away with touching the brake pedal, I think by design.

[Alan in AZ]

Since the brake lights are a primary safety items it wants you to test them at startup. No bulb monitoring works untl the bulbs are supposed to be on - so the stop light message is supposed to make you tap the brakes initially to test the lights and make the warning go out...before ou mode off - its good practice.

Alan

[mtelliott]

Originally Posted by rj7630

I have a very similar problem with my 84S auto. Everytime I start it up the taillight worning light comes on. If I just tap the brakes it goes off and stays off. Not sure what causes this. The tailights all work just great.

That's the Porsche dummy system that tells you to step on your brakes before putting it into gear. It's normal and of zero value to driving the car but for some reason, Porsche made it work that way.

Michael

[mtelliott]

I've also found that when replacing break lights, you should replace all the lights. I had one light that worked, but had a lot of corrosion on it. I fixed the light that was out but the warning lamp stayed on even though on lights worked.

I replaced the other break light and all was fixed.