300TD rear wiper
 

The rear wiper on my 300TD is dead. I get voltage on two pins of the connector and a good ground. Replaced it with one from a salvage yard and it's dead also.
What am I missing? Also, why so many wires going to the wiper. One for the regular speed, one for intermittent and one ground are all that’s needed. There seem to be 5, however. Talk about the Teutonic obsession with complexity!
Can anyone shed some light? By the bye, everything else in the hatch works OK.