My driver's side lock doesn't do anything. I have to lock it manually. (The passenger side lock works just fine, activates the alarm, everything.)

I checked both inline fuses, which were intact.

I opened up both inline fuses. I get battery voltage between the inline fuse contacts of the passenger side. I get no voltage between the inline fuse contacts of the driver's side.

Checking for continuity on the driver's side:
A25 (on the CE panel) to inline fuse: continuity
inline fuse to terminal 13 of the plug on the driver's side (near the driver's side door hinge): continuity
Terminal 13 of plug to pin 4 of central lock motor: continuity
A25 (on the CE panel) to pin 4 of central lock motor: continuity

Yet… no voltage between inline fuse contacts of the driver's side, and no voltage at pin 4 of central lock motor of driver's side.

I took lab electronics in college, and am embarrassed to be asking, but I am stumped.

Thank you for reading!

 

Update

So, there was some corrosion on the inline fuse itself, which was the culprit. (!)

Now, another question:

Driver's and passenger's doors lock with the central console button, and with the passenger door key.

However, unlocking/locking on the driver's side produces no response from the central locking system.

Have any of you ever had this issue?

 

I had this same issue with my drivers side lock. I thought I read somewhere here that if the large black plastic ring that surrounds the manual lock **** or the lock **** itself is screwed on too tight that, that may be the problem. I took my door panel off to add the armrest reinforcement bracket. When I put the panel back on, I made sure I didn't screw that ring on too tight and I didn't screw the **** back on too tight either. The central locking from the driver's side worked since then. Maybe a coincidence, I'm not sure. Somehow those bind the lock? Worth a try.

 

Go with what Rick suggests. If that doesn't do the trick, your problem may be that the bellcrank on driver's side door motor is out of position. The door lock motor assembly drives the lock open and closed but also acts as a switch to activate the lock/unlock cycle when the key is turned in the door cylinder. If the bellcrank (arm on the motor that pulls/pushes) the lock rod is out of position, the switch will not activate the locks when driven by the door lock cylinder. There is a TSB (technical service bulletin) that covers all of this. Do a search for it because it is essential to fixing the lock system.

 

Thanks Rick and Otto for your replies.

Unfortunately the ring and everything else is disassembled (I took off the door panel) so that is probably not it.

I can't seem to find the TSB, although I have the WSM in CD and paper form.

 

Rick and Otto, do you think that if i replaced the lock (with a used unit from 928Intl) it will fix the problem?

I ask because my '86 door locks (both sides) seem to go up/down at 1/4 the speed that my door locks on my '87. It seems that they are both "tired."

Are these units serviceable or should I just buy new ones? I opened one up and it had plastic gears, but the mechanism was held together by plastic welds at the top, and rather than pry it open I've decided to leave it for now. (It does not appear to invite disassembly like, say, the HVAC setting motor does.)

 

Update: The central locking problem- a problem for all six years I've owned the 86.5, is solved.

For other newbies like me out there that are frustrated by this problem, what I did was:

1) I swapped my central locking control unit (it is located behind the driver's side carpet panel, probably to the right of your right shin) with a know 'good' unit from my '87.

2) I tested for continuity using a multimeter for all connections from the locking motor to the CE panel. I discovered that the ground wire on the driver's side was severed, somewhere in the area where the wiring harness goes through a tube near the door hinge. Several other Rennlisters have mentioned that this is a frequent failure point. I wish I had taken their advice much earlier.

That did not fix my problem.

3) Some of the cylindrical (male) metal terminals in the connector were not connecting- they were almost falling out. The reason was that they were not "locked" in. I carefully re-shaped the little barbs that serve to lock in the terminals into the white connector.

That did not solve the problem.

4) I re-checked the inline fuses in the CE panel area. They looked fine, but the driver's side fuse was actually burned out. I could not see the break in the filament- it must have been hidden. Make sure you check for continuity in the inline fuses with a multimeter...

Finally, it worked.

Like many things, it is a bad connection or a failed wire that gives us electrical gremlins.

I bought a used door lock motor from 928 International. It turns out that it was unnecessary, because my old one worked. I'll keep one as a spare.

Have any of you tinkered with these so they turn more freely?

 

You can open it up, clean the contacts and add a little dielectric grease. It seemed to help my motors a bit
although my system still doesn't work. I have a bundle of wires next to my right shin (the area you talked about).
They have all been cut and I think that might have gone to the central locking but the passenger's side lock still works.
Mine is a 1981 model and I don't know if they made any changes during the model run in the electric motor locks.