ajricker

When starting the car . Sometimes the stop lamp warning will not turn off when depressing the break peddle. When this happens I have no break lights no electric door locks and no head lights. If I turn the ignition off with my foot on the break and restart the car it will clear it most times. some times while driving when I step on the break the same thing will happen. Then I have to pull over shut the car down and restart it and hope it clears it. I checked all relevant fuses and all are good. I've ordered a new break light switch but don't realy think that is the problem. What has me confused is three different systems going out when this happens. I thought maybe it could be a relay going bad. But Looking at the chart I don't see one that might cause that issue. Other than that the car starts and runs well. I have also changed out all the stop lights. Also the frequency of thi seems to be increasing.

ajricker

Any suggestions would be greatly appriciated.

Dutch 928 fan

My suggesntions are limited to the fact that the brake warning light can come on if the resistance between the left and rifht brake light bulb is different. Things to check are therefore: corroded bulb or loose lamp fitting on one side, or a corroded contact or moisture on one side. Replacing bulbs on both sides at the same time is a good idea to avoid issues. Hope this clears your issue.

ajricker

That was the first thing I checked. Already changed all three bulbs at the same time. Thanks for the input.

MainePorsche

Art,
Sounds like you have a ground that is getting intermittently corrupted. If you have different systems that are getting a simultaneous malfunction, then I would bet on that. I would look to MP IV under in the driver footwell. This point is the ground point for central locking and your headlight switch. I'm not sure if the brake pedal has a switch which is grounded there, but if it needed a ground point then MP IV would be the closest.
With your DVM check MP IV to see if this point is corrupted when the situation exists. If this is the case you will have some hunting to do, but at least it will be narrowed down.

ajricker

Thanks Craig,
I decided to start checking grounds when I got home this afternoon.
I loosened the bolts hold the ground above the CE panel and sprayed contact cleaner on them. Then re-tightened them. Everything seems to be working fine after that. Time will tell though. If it starts acting up again drivers side will be next.
Do you know if the parcel shelf has to be removed to get to the grounds?

MainePorsche

Art,
I'm not sure about the shelf blocking access for I've taken mine out on the driver's side - I have big feet. I think you might though. First put your DVM lead to the point when the situation exists. If bad then you will have to do the monkey thing and take off all ground ringlets there and check each one individually to find the offender. From there it is then finding where the corruption is in the line. Happy hunting.
Craig

ajricker

Thanks Craig, hopefully I can leave the monkey in the closet. B-)

RET

Don't discount a flakey ignition switch. Try twisting the key while in the on position.

Some bizarre problems have been caused by them. In my case, stepping on the brake pedal turned the headlights off (they did not retract, only the lights extinguished). Quite exciting at night.

Good luck.

MainePorsche

Good point RET.
There are ties in from the ignition switch to lamp controller and headlights. Now a matter of investigation and exclusion.
There is always a learning curve on the 928.

Alan

It is almost certainly the ignition switch - your X bus is not powered when this happens. You will note that the cigar lighter doesn't work either.

Alan

MainePorsche

Always a learning experience here.
I tend to look toward corrupted ground(s) for I've had one wreaking havoc with multiple systems.

Alan

I think the give away here is the brake lights and headlights not working when this happens - the brakes lights don't turn off the dash warning because they aren't actually activated - the brake lights get power from the X-Bus circuit which is direct drive from the ignition switch.

Wiggling the swicth will probably show that the connections are dodgy... get a new electrical switch part - apart from access its an easy change - no need to mess with the lock part. Do get an OEM swicth - there are cheap chinese aftermarket versions that don't last long... Roger can help you out

Alan

MainePorsche

Alan,
Thanks for the pearl.
Craig

jeff spahn

Is the reason this switch gets so warm an indication of all the current going through it or an indication of a cheap switch?