Incident Overview
After takeoff, the pilot detected a smoke odor in the cockpit. He promptly returned to the departure airport, landed without incident, and taxied to the ramp. During the subsequent postflight inspection, the rotating beacon power wire was found to be burnt along its entire length within the airplane.
Inspection Findings
Further examination revealed that a holding screw for the electroluminescent panel had made contact with the rotating beacon switch/circuit breaker, causing the switch to fracture. The switch/breaker was attached to a solid bus bar behind the panel, and the screw was positioned directly below the toggle portion of the switch.
The initiating event was suspected to be a failed beacon motor, which then led to a short circuit; however, this was not positively confirmed during the investigation.
Manufacturer Documentation
The manufacturer's parts catalog specified the use of a particular screw for the electroluminescent panel, but it did not provide a dash number indicating the screw's length.
Conclusion
The investigation documented the physical evidence of the burnt wire and damaged switch, but no definitive cause for the short circuit was determined.