I have a 1987 300E. The central locking system does not lock or unlock when I am using the actuator on the driver's side door. However, the entire system works just fine (including the lock on the driver's door) when it is activated from the passenger side door or from the trunk. Therefore, I think this is not a vacuum line problem, but an electrical problem. I tested the electrical function of the driver's door actuator, and it's voltage supply - both seem OK. Where do I go from here? Your technical wisdom here would be greatly appreciated.

The locks on Mercedes are a pain to troubleshoot since they are both vacuum and electrical. I had the same symptoms as you did. This is what was wrong with mine. The trunk actuator was broken. I just replaced it with a good one. Also the hose that runs through the trunk lid to the trunk actuator had a splice. This is a common thing, I have seen it on several Mercedes. The hose runs through the right side of the trunk lid and can apparently get spliced. I just cut the line and put a rubber hose over it to reconnect it. Since then my locks have worked fine. Who would have guessed the trunk actuator was bad when I couldn't open the locks from the drivers door?

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Adrian Eckenrod
MBCA, PCA, BMWCCA & SCCA* member
86 190 2.3-16
83 944 ITS Racer

The driver's door has two sets of switches and one is located on the actuator the other is located on the door handle. will your door unlock with the key from the driver's side and will it unlock from the inside??

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Sounds like a vacuum leak somewhere in the system. Check for vac. leaks on the lines as they pass from the body of the vehicle to the door. Over time the constant opening and closing of the door is enough to break the plastic lines. Good luck!

Thanks for the discussion & suggestions. As it turns out, there is a "control line" (blue wire) that goes from the driver's door actuator to the supply pump under the rear passenger seat. In my car, the wire had been interrupted somewhere. We put in a new wire, and voila! Everything is now working, and the world is right again.