Vacume Locking System Problem

[Leewolf]

I have both a 1988 300SE 4dr and a 1988 560 SEC Coupe. Whatever ails one of these cars will within weeks ail the other. I think they are joined at the exhaust pipe or something.
Anyway, The vacume system on the Locking system in the 300 SE failed and after checking out the pump, wiring and a couple of other things it turned out to be a leaky vacume line.
The same sytem has never worked (since I have had the car) on the 560 SEC. This car has essentially the same system as the 4dr but obviously has only two doors. On this car the pump had failed. Nothing we could do would make it work. An outside vacume source did work all the locks etc. Got a new pump (it definitely works) and CAN NOT GET A SIGNAL FROM THE DOOR LOCKS TO THE PUMP!! (or for that matter, from the trunk lock)
The wiring diagrams indicate one set of colors for the wiring but the wires at the door locks are not those colors. There is more.
We unpugged the anti theft module since all the hot wires from the door switches go there (parallel connection). This did not help. We've traced wiring at least until it dissappears into the chassis. Bottom line, the ground side seems to be the culprit but all connections seem to be OK. Does anybody have any ideas or experience with this system and could mabey shed some light or point us in a direction. It appears that the polarity of the current is is some way switched to change the pump motor direction, could this be , and if so, how?? (if this is pertinant to the problem)
I have the car with a local mechanic, He has worked sucessfully on all four of my older MBs. I live about 120 miles from a dealer and kind of depend on some help from my fellow MB owners at the forum.
Thanks for any help
Lee
Also have a 1980 450 SLC 5.0 Euro