The 300SD would be a very different system than those described above. It DOES NOT use engine vacuum. It uses a bi-directional pump that sucks and blows. It uses a single air line to each element.

The pump is in the trunk with the spare tire. It is activated by only the drivers door (I think on an 83; later years worked from the pass door and trunk)

Actually I checked and there is one switch in the drivers door. It carries power from fuse 13 through either a blue wire for lock or a yellow wire for unlock. This should be monitored at the pump while someone works the lock at the door.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician