Alan:

I found the matching connector in the Schematics. MY1990 Sheet 2 location L3. "Lights central electric."

Where does this plug into? There is no hacking here. The connector is just not plugged into anything.

And this "Lights Central Electric" connector does have something to do with the alarm because when tracing the BR/WH wire, it leads to position M67 on Sheet 5 which is both the alarm control unit and additional alarm control unit.

How does all this work together? If I can find where to plug this connector in, all the problems might just go away at once.

I've given the exact location of this for all to see for themselves. Just need help plugging it back in somewhere.

 

You should have a light (a simple fitting with festoon bulb) a over your central electric panel - it plugs into that.

While it should be connected - it has no bearing on anything else

Alan

 

On your year you have the most complex set-up (was quite rationalized in the following year).

You have up to 3 alarm units (optional features) and a Central Locking control unit and an interior light delay relay, these were all later merged into a single unit in 1991. It is likely in a USA car that it was originally delivered with all 3 alarm modules

They do more or less as you would think (below is year specific)

Interior Lights Relay is just interior lights

Central Locking Module controls locks and central lock button

Alarm Main is the main alarm unit controlling the alert horn/ ignition disable

Secondary Alarm adds addional monitored features / LED posts over earlier versions - M533

Alarm Relay allows you to have the lights flash as well as the horn honk (optional) M533+M484

Interactions:

The lock & unlock from the door key locks go to both Alarm and Central Locking (e.g. Open & Disarm; Lock & Arm).

The unlock/disarm from the rear hatch goes only to the alarm while the lock/arm goes to both alarm and central locking.

The alarm unit also monitors the lock drive state that also goes to the central locking - and monitors interior lights for the hatch monitoring

Note the alarm alert for the doors first goes off when the doors are unlocked - when not disarmed (by turning the release ****, raising the post, levering the lock components or forcing the lock) - before the doors are actually opened.

The later versions '91 & up also added alarming similarly even if you successfully pick a lock. (assuming you don't succeed in picking both the normal lock and the secondary alarm tumbler section). If the switched interior lights come on when armed - the system will alert - but this is primarily to protect against entry via the hatch - since it has no lock state to monitor.

Alan

 

I have all of the above you mentioned. Makes for a more complex process of analysis. Typical over engineering of the 928.

Back to that "lights central electric" plug. Okay, so it is only for illumination of the CE panel. If the festoon gizmo is missing, as you say, it has no bearing on anything else. As long as you are sure, okay then.

As to the other "unplugged connector" I did discover it is the "Potentiometer Not Applicable with Cat. Conv." Sheet 10 location O & P 88. It's actually a three pin connector but only two wires are used. It is likely just a part of the universal harness that many 928's were fitted with even if they never used this plug. So this is also non related.

What's left? Nothing I can see as I have gone through both ends of the under dash and main harness and smaller harnesses. It could therefore possibly be a bad ground or an open ground thereby keeping the doors from locking using the central locking button. Remember, they open no problem using the central locking button. They just will not lock. Every time you press it, you just hear the fast triggering of the lock cylinders firing the locks open even if they are already open. And only with this button as they lock using all the lock cylinders (doors and hatch) outside the vehicle. The button illumination remains brightly lit all the time.

Strange problem.

 

That light over the CE panel. I looked for it in the Porsche PET parts catalogue and could not locate the part to order. Does anyone have a part number and a photo so I can get an actual visual?

Thx.

 

UPDATE... now that time has permitted this winter project o be complete...

The problem of central locks and alarm system LEDs got resolved at the same time with ONE solution. I know how common it is for many 928 owners to focus too heavily on something electrical as these cars can be electrical nightmares. Just not this time.

After extensive electrical diagnosis, it was discovered that the driver's side door panel needed to be removed. Sure enough the left side door lock pin needed to be adjusted as it was binding during the central lock button depression for the unlock procedure. Once this mechanical adjustment was made, central locks and alarm LEDs work normally as there is a direct relationship with the locking system and the alarm.

Interestingly, the alarm horn is fried. But that is something likely not to be fixed as the location to swap it out is too awkward for something as trivial as this.

Hopefully this will help someone else who runs into an identical problem.

 

I came across this old thread regarding the central locking system light on the panel staying lit when unlocked and the LED in the door lock stem flashing as though the alarm system was activated on MY 90 GT. I had just got the car out of the paint shop because the door and other parts were resprayed. I figured they must have been inside the door to remove the door handle since the paint was done very well. As stated in the post above, an adjustment was needed actually on the power lock actuator. Since I saw the two bolts in a slotted holes, I figured there must be an adjustment . I slid the actuator toward the back of the door, the door would not lock with the key. I slid it toward the front and I heard the quiet click of a micro-switch and the light in the lock stem went out. So I knew I was on to something. I played around with various positions and found a sweet spot that allowed the lights to be off on the central panel and the door stems along with the key locking and unlocking. Alarm works arming and un-arming. Thanks Kevin R.!

 

+1 Was fighting an door stem blinking all the time and central locking button always on (1989 S4)

Adjusting the lock actuator cured it.

Thanks to Kevin R. for his post.

 

I have a 1984 standard USA model 928. My doors both lock and unlock with the key from either door, but my central locking button does not work anymore to lock or unlock. I changed out the button panel itself (found two disconnected wires on the back of the old one), and the central unit by the drivers right thigh under the center console. The lock light does not illuminate anymore either. What is the consensus and has anyone else had this issue?
Thanks in advance!