Dieselbenz1,
thanks for the hint! I can see at the rear of my pump a two-pronged electrical connection which is filthy from never being connected. For the life of me, I cannot find any unconnected wire which should be plugged there.

Do you know where these leads would originate from, or how to find them in the engine bay?

My 190d is 1984 (the first year) and all the diagrams I can find of the IP show a vacuum pot in these location, not an electrical connection. I wonder if my IP was replaced at some point....
but then again, I don't have any un-connected vacuum connectors either. Wierd.

Thanks All!