As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) PILOT REPORTED THAT FLIGHT CONTROLS WERE (STIFF AND VERY HARD TO MOVE). DURING RUN-UP PRIOR TO DEPARTURE. PILOT ELECTED TO RETURN TO BASE. AMO FOUND THAT WIRE HARNESS BEHIND RADIO PANEL WAS CHAFING ON THROTTLE MOUNT CAUSING SHORT TO GROUND. THIS CAUSED THE AUTOPILOT SERVO TO ENGAGE UNCOMMANDED.