I just posted the below in another thread...
Once you get the motor to run, the next issue you will no doubt have is is that the wiper blade only contacts 60%-70% of the rear glass. This is because the motor is mounted in rubber grommets on the thin sheet metal of the lift-gate. This causes the force of the spring of the wiper arm to twist the motor in it's mounts. If you look at the rubber boot where the motor's stud sticks through the lift-gate, you'll see that it's pushed to the left, where it should stick out straight from the center. After a while the motor take a permanent set, then the geometry of the wiper arm to the glass is thrown off when the blade is on the passenger side. I've read about and tried several supposed fixes for this, but I find that the only one that worked pretty well for me was to cut the stops on the wiper arm (with my Dremel tool) to allow the arm to get closer to the glass. I also get better results by using an expensive Bosch Evolution rear blade, cheap blades tend to get stuck in the gap between the glass and lift-gate, once the arm tension on the left side is increased. I find that after cutting 1/16th to 1/8th of an inch off the wiper arm stops I get 90%-100% blade coverage on the rear glass. I've made this mod on 4 Expl's/Monty's with the same success rate.