CHolmes

My 87 300D's central locking is driving me crazy, literally, when I got the car it worked but not well. It had a few leaks so I fixed all by changing the drvs door, trunk and fuel flap lock actuators. Worked perfectly so I added the keyless system and again it worked perfectly for 2 or so months. Then yesterday driving along it locks on it's own for no particular reason. I tried it a few times and always the same, although the time it would take varied. I put it in the shop thinking something frozen and tried it a few times and then it stayed unlocked. This morning it doesn't work at all so I pulled the seat and checked it out. There appears to be no 12v at the connector. Fuse is good, no problem there, no leaks at all, pump will run if I connect 12v to it but it will do the same thing, the keyless will work as it should but when I unlock it it now will immediately lock. I tried it several times, the drvs key will not lock or unlock (with the pump) and it always did. So I am baffled, it makes no sense unless it is the drvs door actuator stuck in the unlock position but that still doesn't explain no 12v at the pump. I vacuum tested, no leaks.. Does anybody have any idea what is going on with it? It seems so simple but apparently not so much.

dolucasi

I have not had to diagnose central locking system in the past 35 years I owned my car, this is partially because on some friend's advice I installed a keyless entry which is super easy 7 years ago.
It saves the actuators and tumblers and such. And it makes locking and unlocking a breeze for under $20.

Sorry, I can not be of any help other than keyless advice, assuming you do not have that installed. And depending on your issue and no vacuum leaks are present it may even solve your issue if you can make the locks work if you manually turn on the pump.

- Cheers

CHolmes

It has keyless