2004 Matrix rear wiper diagnostic?

[sPksail]

My rear wiper on my 2004 Matrix works periodically. It usually doesn't work. The fuse is good. When I hit the motor with my hand, it started up so I think it is something in the back of the car rather than the switch on the steering wheel. I took the rear wiper motor assembly off but don't have a wiring diagram to test properly.
Does anyone have a wiring diagram or can tell me which color of wire is which? There are four wires, it looks like black is the ground. Any other help in diagnosing or fixing the problem would be helpful.

thanks,
sPk