Does the motor stick or does the electric power not get to the motor? Take the assembly out of the car and hook it up to a battery, a 9 volt was big enough to move mine a few times.
If the motor is stuck, you need to buy a new one (ebay?) or rebuild it.
If the motor moves, then you need to check your wiring, mainly your relays. There are 2 that can go bad, a main for both lights, and one for each light.
I replaced my relays, the motor moves up, but forgetst to come down. I'm going to check the wiring for it because I think the old wires are losing connection.