If it is the main light that is flashing it is a door sensor problem. Did you remove the wires from the rear of the motor unit when you replaced the gear? If so you may not have put the wires back where they belong. The solid white wire from each sensor goes to terminal #2 and the white wires with the black stripe go to terminal #3. Make sure the door sensors are pointed at one another and the small light on each one is lit and not flickering. Tweak them if necessary.