If the pump doesn't make any sound as the doors are locked or unlocked then it's probably an electrical problem as you suspect. There are 6 wires at the supply pump:

- black from the orthopedic seats (if equipped, what for?)
- red with black power from fuse (13?)
- blue from driver's lock
- green from passenger's lock
- yellow from trunk lock
- brown to ground

I doubt that you have to be concerned with the black wire since you probably don't have orthopedic seats... or a black wire.

The red wire with black stripe should see a constant 12V.

The brown wire should have continuity with the chassis/frame.

All of the lock wires should see 12V when the door is unlocked and continuity to ground when the door is locked. Any one will act as a trigger.

Good luck.

Sixto
91 300SE
87 300SDL
81 300SD