Without seeing it, my guess would be that when it was dropped, the wiring to the socket was disturbed or distorted in a way that causes the short circuit to occur only when the bulb is in place. Try measuring the resistance across the lighter plug terminals with and without the bulb. If there is an "On/Off" switch, take the reading both ways. Then compare it to the same reading taken when the bulb is in the socket. With the switch in the "Off" position (If there is a switch) the reading across the terminals should be infinity (Or "OL" for DVOM's). With the switch on, you will read the resistance of the rotator motor, whatever it may be. With a properly working unit, the reading should be a little lower (Because the bulb is in parallel with the motor) with the bulb in place, but not "0 ohms". 0 ohms under these conditions would indicate a dead short caused by the condition I described. You would then have to disassemble the unit and inspect the wiring to the socket with and without bulb in place and make repairs accordingly.