central locking
 

After replacing the window regulator of the driver door on my 91 420sel,i lost the central locking on the back doors(will open,but not enough power to close them)also when opening the driver door only,the dome light and courtesylight and the memory seat will not work.However if I open the passenger door or turn the ignition on,those item are working(except for central locking system).I suspect a wire problem in the door.What wire could it be and how do i test it and fix it.I notice the wires go somewhere behind the dash,how far do I need to go?

Sounds like you might have two different issues here. As you probably know, the locks are operated by vacuum rather than the typical electric actuator. My guess is you pinched, cracked, or snapped a line in the driver's door which is causing the whole system to lose vaccum pressure. The lines are small hard yellow plastic and are fairly unflexible and brittle. Take the door apart and see.

As for the lighting / seat issues this is the result of a failed seat belt relay. My car had (still has) this problem (1995 E320) I'm sure its the same for you. On my car (w124) the relay is located behind the instrument cluster, $60. Check the contact switch out on the driver's door just to be sure that's not the problem (swap it with another from any other door--easy) The seat belt relay makes the red fasten seat belt warning come on when a door is open. On the driver's side, it also gives power to the contact switches making the lights come on, the seat work, etc. Same as my car. That's why they work with the pass door open, which has an independent circuit.