Christopher Zach

This is weird: So I have been finishing up the prep work for my 1986 928S to pass MD inspection. One of the headlights was loose; problem was the lens had seperated from the bulb. Turned off the car, brought the lights up with the ****, replaced the bulb, no big issue.

Now things are insane. Here are the symptoms:

• Headlights do not go up and down anymore.
• Low beams do not work at all.
• High beams do work when I push turn signal forward to high beams
• High beams flash when I pull the turn signal
• When turning the headlight switch to park, running lights come on, one set of fog lights come on, parking lights green indicator comes on the dash.
• When turning the headlight switch on, parking lights green indicator goes off, running lights on, one set of fogs on.
• Putting on the high beams turns on the other set of fog lights

I tried replacing the headlight control relay with a new one and things still don't seem to work. Worst part is this makes no sense; the relay should be allowing low or high beams to be on but the default (non energized) is low beams. How can they not work?

Is there another relay that sources power to the lights, and is there a way to test the headlight motor to see why it's not going up/down anymore? It's like the car went bannanas or something.

Thanks!
C
(PS: checked the fuses, they looked good)

Christopher Zach

Figured it out. And since this will bite someone else in the future I'm putting it down here because Porsche was silly in the way they did this. Anyway, here it is.

From the most basic question we can fix this using a trouble tree. Let's start at the top:

1) Am I insane?
No. I am under a psychiatrist's care and he assures me that I am sane. Therefore there must be a cause.

2) Are the lights insane?
Possibly. Let's start by seeing if we can hot wire the lights to come on.

From the wiring manual I can see that the lights are powered by +12v being applied to either 56a for high beams or 56b for low beams. Thus if we can hook pin 30 (the real one) to 56a or b the lights should come on.

Test: Hook probe to 56a, set to 10a current. Jump as spark from other probe touching frame scares you. Realize that 30 is always powered. Respect this. Connect 30 to 56a, 9amp draw, both high beams on. Connect 30 to 56b, 8.5 amp draw, both lights on. Disconnect.

Answer: Headlights, fuses, wiring, bulbs, and the like are ok. Problem is somewhere else.

3) Is the common from the headlight relay going to pin 30 or 30a?

No, according to the wiring diagram it is not. Hm. Why?

The input to the common of the high/low relay is driven not by 30 directly, but by an internal path to a third relay which I will call Relay 3. This relay switches power between 30a (the +12 that is on when the key is in) and the headlights.

So how does this relay close? Well, one end goes to the morass that is called the Transistor (IC logic, I'll figure it out later) and the other end goes to 30a. However 30a does NOT go right to the +12 line it goes through a fuse called fuse 27.

Which is the headlamp motor lift fuse. Checked the fuse, it was good, but when I tested for +12v with the fuse in and the key on I got 0 Volts.

AH HA!

The problem is that my fuse assembly is not in good shape, and some of the fuses (two so far) are not making proper contact in the back. Wiggling the fuse makes the +12 appear. Putting in a small shim between it and the next fuse provides enough force to hold it in and hold +12 on 30a. Which when I put in the headlamp relay assembly immediately brought the headlights down. Turning on the headlight switch now brings the motor up and lights the lights.

This IMO is a very bad design: If your lift motor were to short out, your lights would go dead out and there would be nothing you could do about it on the road: If you replaced the fuse it would blow again. And since the fuse also provides the gate power to enable the lights, you would have no lights other than fogs. Which I found in a massive rainstorm last week are not enough to keep you safe on the road.

Ug.

So be warned: If everything in the headlight system looks insane check to make sure power is getting to pin 30a from fuse 27. It's possible the fuse is bad or the holder is bad.

Next up: I'm going to have to pull and rebuild the whole fuse assembly. Any tips on R&Ring the connections?

Meantime it should pass inspections. I'm debating a temporary hard bypass of that fuse by installing an external fuse by soldering to the relay 30a pin directly and to another relay. But it looks like I will have to pull the whole box and who knows how many other fuses have similar problems when disturbed...

drscottsmith

Chris -

One of the first things I did when I got my non-running car was to pull the CE panel and go through it. Fixed a number of things in the cabin and I am sure contributed to getting the motor running faster.

I cleaned all the fuse holders with a cleaning wheel on the dremel. Cleaned all relay tabs as well. Also cleaned the receiving connectors in the panel itself with Deoxit.

Check for any receiving tabs that have been pushed through the back of the panel, as well as any corroded or burned wires and replace as necessary.

It is a lot of work, but you can fend off MANY more electrical gremlins later on knowing that the CE panel is working as designed.

-scott

Christopher Zach

Indeed. I take it you have the earlier style torpedo fuses, I think they made better contact than these blade style ones. My main reason to not pull the panel is because I don't want to make thing worse at the moment until I get the car inspected. :-)

Was it difficult to remove overall and any specific gotchas to watch out for?

drscottsmith

Not too bad -

Make sure to release the locking tab before you start removing the connectors across the bottom of the panel.

Pull the connectors - I labelled mine but they are color coded and you really can't get them wrong. The number of pins usually varies also.

There are a number of red wires that feed the panel 12V - dont forget to disconnect those. There are two ground points above the panel that have be be disconnected as well.

Don't forget to disconnect the negative cable at the battery before you start everything.

I have an '83, BTW...so I do have the torpedo fuses. I hope everythign I have mentioned is the same.

skpyle lives near me and he pulled his panel awhile back. I think his car is an '86, so he might be able to provide additional insight. Super guy and a great source of info.

-scott

JPTL

Hey Chris, completely off your original topic, but will we see you at Frenzy at the end of September??

Christopher Zach

Poof

Christopher Zach

Depends. If I can get my timing belt tensioned then I will attend. Right now my fave Porsche place says they won't work on 928's, and the belt ten light came on when cool and over 4k RPM. So I'm restricted in driving it now. Drat.

Alan

The blade fuses are in fact much much better for general contact than the torpedo fuses which are the ones that typically have lots of issues. OTOH - the torpedo fuse holders are much easier to clean when there are issues.

Only the highly loaded ATC fuses (30A esp. for cooling fans) have major problems - and usually this it is related to corrosion from water dripping on the panel.

Alan

skpyle

Hello Chris,

Please refer to posts #45 through #53 here for details on R&R of CE panel:

https://rennlist.com/forums/928-foru...d-witch-3.html

Christopher Zach

This one's a bit batty; the 30a one for the front fan is melted (I think the previous bozo had a shim in there for his stupid car cell phone. Rich enough to have a cell phone in his CAR I say!) and the 15a one for the headlights needed a bending of the tabs to fix.

Pulling the panel and replacing one of the clusters of five fuses is on the to-do list; I just have to find that round tuit in my tool box. I think I will do that in the winter along with getting a new compressor (current one is in poor shape; can only pump to about 250psi and I need to do a proper R134a retrofit anyway with new oil and such), just do these things while snow is on the ground and the Porsches are sleeping snug in the driveway.

C

Christopher Zach

Thank you for the link Skple: That whole thread seems chock full of good information. Reading slowly....

skpyle

You are quite welcome, Chris.

I am slowly chewing through a laundry list of issues with my 1986.5, some big, some small.
The Red Witch will be back together at some point.
I have several posts out there as I DIY my 928 from the perspective of a home hobbyist mechanic.

Alan

IMPORTANT

Be aware that the fuse blocks vary by more than the printed numbers & colors. There are internal buss bar fuse-fuse connections on the input side that vary by year. Some have all 5 fuses shorted, some have pairs of 2 and some have other configurations. These are not consistent by number by year. So you need a fuse block of the same number range from the same year CE panel or you need to check the config and have spare terminals to be able to reconfigure it.

See previous threads on this topic

Alan

mj1pate

Chris; since you mentioned the base concern is passing inspections; have you checked into "Historic" vehicle registration in Maryland?
My 86.5 has Maryland Historic plates and I had to endure no types of inspections in order to register. Maryland does have a mileage limit on Historically registered cars.... but no one checks. The state has left me alone for 10 years.