Okay, I'll try to give you guys the short version of the story. This problem has existed for 2 years now, and I'm finally determined to take care of it.
About 2 years ago a body shop replaced my driver's side door (1987 560SEL) which was the victim of a hit and run while I was at work. A while before the hit and run, someone (an enemy or a random jerk) put glue in the keyholes of my driver's and passenger side doors. Since then I had been using the trunk to open the doors until I got around to replacing the door handles. Since the car was already in service for the hit and run, I had the shop put in a new driver's side handle/lock. When I got the car back everything looked great (well, mostly), except that my central locking was no longer functioning correctly.
When I use the key in the driver's side door (the passenger side has not been replaced, so no way to test that) everything works as it should. Either all the doors lock (including trunk and gas) or they all unlock. However, when I get into the car and depress the lock knob thing the central locking does nothing. No pump sound, only the lock that I depressed goes down.
Logically, the problem has to be somewhere which would have been removed/replaced with the door, however I simply cannot figure it out. I was under the impression that the central locking is activated when the lock knob goes down and makes/breaks contact with something. I guess it is more complex than that or I wouldn't be having this problem. Any ideas where to start??

Here are some additional details if they will help anyone figure this out...
1) When depressing the passenger side knob all the doors will lock if the ignition is in the "0" position (normal)
2) When depressing the passenger side knob, none of the others will lock if the car is running, however when the ignition is turned off following this action, all the doors lock. (not so normal)
3) If I lock the doors from the passenger side when leaving the vehicle (like I have some stuff in the passsenger seat...), when I return and unlock the driver's door (with the key) none of the others will open (and the knob tries to "suck" itself back in sometimes). If I unlock/lock/unlock in this situation, everything returns to normal.
4) If I unlock the car from the trunk, all doors and the gas flap unlock. If I lock the car from the driver's door after that none of the others will lock. Again I have to lock/unlock/lock.

I think that's it. If anyone needs more info, let me know! I'll get a case of beer for whoever can help me get this fixed. (no, seriously.)

Hello Justin,
Sounds pretty messed up, that.
Let's start here: Your central locking system is electro pneumatic. A pump in the spare wheel pan either pressurizes (opening) or vacumizes (locking) the individual central locking elements in the door shell. These same elements in FL and FR door and in the trunk contain also the switches. All switches have a 3-pin connection.
Your vacuum system seems to be ok. Once you lock/ unlock the vehicle, all elements work and the pump won't run for more then 5 sec.? Right?
What must have happened is, that when your door was done, the connector to the element fell apart. They love to do that. They just crumble away. Then the guy mixed up the 3 pins in that same connector. So have a look if that connector is still original.
Also correct the rod adjustment in the element. It's probably in too deep.
Go fix it.
All the best.
Dokta

Thanks for the reply Dokta. I believe that the connector is still original (I think it's a circular white plug with one flat side??), I'll get the door panel off and remove the element and check the rod adjustment. The only thing that still puzzles me is why there are problems on the passenger side if the source of the problem is the driver's side element (or its connection.) Is it possible that there is a controller or relay somewhere that got fried during the uninstallation/reinstallation?

Hello Justin!
There is no relay. All switches are wired into the pump. When the FL locking element is undone from the rod, simulate the up-down action. Be careful with the locking sleeve for the rod; avoid pulling it up. It's difficult to open without the rod installed.
Now, if the connector is installed properly, it should easily lock/unlock. Note that it is even possible to push the connector in with the end twisted by 120/240 degree !! The element wont lock the connector properly then, but I've seen it!
Check it and get back.
All the best,
Dokta

allright Dokta, I'll get the panel off tomorrow hopefully, and we'll see what we can find. Just to verify, the alarm control unit under the passenger side footwell and the S8/2 thing attached to the steering column have no effect on the operation of the central locking??
Also, since there are 2 switches on the front doors, does the bottom one have anything to do with central locking/alarm operation? The top one seems to handle the dome/door lights and seatbelt warning buzzer, what does the bottom one do?

Hello Justin,
The alarm doesn't have to do with it. The activate/ de-activate micro-switch is in the door handles. The column switch is just a buzzer (key in lock).
I believe the bottom a-post switch does the alarm (not sure).
But the central locking ought to work totally independent from the alarm. I disconnected a lot of alarm ctrl. units due to trouble and never came across any interference.
All the best,
Dokta

Alright, I finally found time to open up the door. Here's what I've got...
I removed the vacuum actuator and swapped the wire harness with the one that goes to the handle/lock mechanism. The result is that the actuator now works as it should (as in I can lock all doors from inside the car), but the key will now only lock the drivers side door (mechanically.) Logically the problem must be with the wire harness. I do not have a multimeter with me, but I assume that I'll need to trace the harness back anyway.
Does it matter which one goes where (lock mechanism, actuator...??) The one that doesn't seem to work has yellow/green wires, the one that does has red/blue wires.
Hopefully someone can answer this soon before I tear up the whole car tracing this wire harness
thanks
justin

Oh yeah, here is a picture of the two harnesses

Attached Thumbnails

 

Hi Dokta: It seems you know your way around this system. My problem is, with all doors unlocked if i push the trunk button everything locks all doors and the trunk. Any suggestions?

Hi 420,
??? No clue...Sorry
Dokta

Hello Justin,
why harness? If you lock the button of the driver's door and all doors lock, the harness is OK. Remember that the switch is in the vacuum element and lock tumbler (key) as well as knob (rod) work the same vacuum element in the driver's door!
All the best,
Dokta

right, what I'm saying is that the electrical plug that was going to the door handle works, and the one that was going directly to the vacuum element doesn't (or doesn't seem to.) When I swapped the plugs (from vacuum element to handle and vice versa) the problem "reversed". Now the knob insidee the car works and the key does not.

Hello Justin,
The micro switch in the door handle is only for the alarm. The switch in the locking element is only for the central locking.
(correct me if I'm wrong)
All the best,
Dokta

Heck, I don't know!

What seems to happen is this:
With the "good" harness plugged into the white plug that comes off of the handle everything works fine with the key. Turning the key seems to send an electrical signal to the pump to either lock or unlock all elements. With the "bad" harness in the actuator, pushing down the button obviously locks the driver's door, however no signal is sent to the pump, therefore nothing else locks/unlocks.

When the wiring harnesses are switched, the key turns the lock, and the lock goes down, but no signal is sent to the pump. However when the button is depressed, the signal is sent (through the "good" harness) and alll locks respond as they should.

So it would seem that the problem is with the yellow/green wire harness, however it has been difficult to find where it goes, or why it is not "active".
justin

WAIT!!!
I'm being stupid. All of this testing has been with the actuator disconnected from the door frame. Locking the door with the key hasn't been able to physically pull down the plunger, only lock the actual door. Swapping wire harnesses (the good one to the actuator) should fix everything (except the alarm, which is more of an annoyance that anything else.) Give me five minutes...