Hello all,

My 1992 400E (205k) has recently developed an interesting problem: Using the key in the driver's side door will no longer lock or unlock any of the other doors. Using the key in the passenger door or trunk will unlock and lock everything as usual (including the drivers door).

Pushing down the lock button from inside the car has the same result: The driver's side will only lock and unlock itself, while pushing down the passenger side will lock and unlock everything.

I have ruled out any vacuum leaks. The pump under the rear seat operates normally and quickly. The problem is that it's not even activated in the first place by the driver's door. So, I have removed the actuator in the driver's door. The resistance values check out O.K. when I test it. Also, the electrical connector is supplying it with 12V, so I'm fairly certain this unit is alright.

The switch that is attached to the door handle itself also seems to be O.K. So, is there any explanation as to what could be causing my issues? I tried jumping the switch connector to see if the doors wold lock/unlock, but all I get is a faint ticking coming from the convenience control module area. The vacuum pump does not actuate. Is there some mystery fuse, or a connection somewhere that is prone to failure? The fuse under the hood is good.

Thanks for any help!