I had to replace a motor mounted on a window regulator (the scissor looking assembly that moves the window up and down) on a 95 windstar a couple of weeks ago. If you have power to the plug at the motor, the motor is bad. There are two pins on the plug. Hook up a meter to the pins and you should have either a +12 or -12 volts, depending on which direction you are pushing the window switch. If that's good, replace the motor. Take note of how the coil spring is mounted on the regulator, and be careful because the motor gear is spring loaded. You'll need to remove the regulator assembly (along with the motor) completely from the door. This isn't the easiest job I've done...
You may need to drill out rivets that hold the regulator inside the door. Use bolts or replace with strong pop rivets when you go back together. Hope this helps...