I think I might have this problem as well. When I bought the car (used), the rear wiper wasn't working, so at first I thought it was just a bad wiper motor. Nope.
The strange thing is, I can measure 12V at the wiper connector, so the wires can't be completely broken. I guess either the wire is frayed enough that there's too much current draw with the motor actually connected, or maybe the ground is bad.
Either way, I might take a look at the harness this weekend before I have the dealer look at it on Monday.