I have a 1986 928S with an odd problem. The stop lamp warning light goes out after the first touch of the brake as normal. During a very short drive, the warning comes back on, the brakes light won't function, the fog lights won't light up and the motor for the headlamps won't activate but the lights activate). All the other lights seem to work.

Any ideas?

 

Alan might can add up the sum of the parts and come up with a solution, but the rest of us are going to ask if you have verified that every-single-ground-point is clean and secured. If not, you need to start from there.

 

Yes, that is logical start. Now I have to learn where all these ground points are located.

 

search on the web via Google. Hate to say it, but it can be more efficient than searching using the forum thread search tool, but yes, use both methods.
Also, as I recall the manuals that comes with the 928 owners club provided shop manuals/electrical diagrams shows the physical location of ground points.
Can someone please advise Periokid how the shop manuals are available for club members these days?

 

Go to the "New Visitor" thread at the top of this Forum and scroll down to post #33. You'll find what you need there.

 

I think you have a failing ignition switch (failing electrical part). The X bus output appears to be becoming intermittent. If this happens again - wiggle the key while it is in the run position and see if it restores operation.

The headlight motor, brakes, fog lights, turn signals all rely on this switch output to operate in run and accessory mode (so you could also check operation stability for these in the accessory mode of the ignition switch)

The electrical part of the ignition switch can be changed relatively easily, it screws on the back of the actual key/lock element - see other threads on this.

Alan

 

Thank you for guys. I appreciate the information. I checked a few grounds before seeing Alan's post. I'll play with the ignition switch.

 

Ok guys, I have an update.

Playing with the ignition key did not make any difference.

I did notice that when the headlights are on (they won't pop up as previous stated), when I hit the brake pedal, the headlights go off. Once I release the brake pedal, the headlights go back on.

Strange.

 

You can test to see if the X-Bus is active - measure the voltage at the top of any of the fuses 1-5. (NB on your model year) Test between ground and the top dimple in the fuse body. With accessory and/or ignition on you should have battery voltage there.
Fuse 3 should be empty? if so you can insert a quick connect (0.25 inch) male connector in the top fuse blade slot for easier access.

Alan

 

I never got to the x-bus check but I just had to move the car and played around a bit. Some observations.....

1. I moved the steering column up and down and also reset the odometer and now everything is working.

2. Resetting the odometer causes a notable click behind the gauge pod and a significant voltage drop occurs (with dimming dash lights). Happens at every push of the button, even when the odometer is at zero.

Is the odometer reset connected to something electrical? Moving the wheel and dash pod, maybe a short somewhere back there?

I am not sure if the odometer reset or the moving of the pod was the fix or just a coincidence but I leaning towards not.

I also have something hanging from the bottom of the pod. it is taped closed and wired to something under there. I am going to get a photo for a possible ID.

 

Here is the item under the pod near the lever to release the steering column. It is cylindrical has three wires.

 

Any ideas? is the odometer supposed cause a voltage drop on reset?

 

The picture is the connector for the rear fog switch that is only used on ROW cars (its a standard loom for both). It is normal for it to be taped up on a USA car.

The reset is electrical via a solenoid so that is relatively normal. Do the tests.

Alan

 

OK, Alan, bringing this one back. I did the x bus check and it is active.

I have full time loss of brake lights, power windows, power sunroof and headlight motors.

Car runs fine otherwise.

So puzzled.

 

THIS...

Seems counter-intuitive but this was absolutely the problem when I had all of these weird issues at once.