Easy to check in the car, measure for voltage at the motor when you turn on the headlights. If voltage is at the motor and it doesn't move, you have a bad motor probably. There are three relays for the headlights, one for each side, which you can swap to isolate the problem. If the problem moves to the other side, you have a bad relay. there is a third isolation relay which supplies ground to the system and switch but I would suspect that would affect both motors. Could be a connection going from the isolation relay to your inop motor. Again, use a meter to isolate and trace back to the cause.