It sounds like a bad switch. To be sure, you need to remove the door panel and check if there is power going to the motor when it isn't working. If there is power, then the motor may be bad. Regardless, based on your description, it sounds like a bad switch if it moves further than it should.
Let me know if you have other questions.
Joe
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Saturday, August 7th, 2010 AT 11:01 PM