http://www.bfranker.badz28.com/headl....htm#FreeGuide
This will walk you through the installation.... basically, what happens is the plastic gear becomes stripped inside the assembly. The design of the motor only uses half of the gear, so you can take the assembly out, and flip the gear around to use the good side. Easy and simple fix that will take about an hour, maybe longer if you really take your time.
Some Signs of a stripped gear:
Grinding sound when headlights are raised or lowered
Activation of alarm (lock doors) will sometimes cause headlights to pop up and down, then grind