As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) WHILE ON GROUND AND ENGINES RUNNING, HEATER WAS SELECTED ON. SMOKE AND SMELL EMANATED FROM UNDER THE INSTRUMENT PANEL. MASTER SWITCH TURNED OFF-NO SMOKE. RE-ATTEMPT MASTER ON - HEATER FAN STARTED BY ITSELF WITH HEATER SWITCH TURNED OFF PILOT FELT SWITCH TO BE HOT. UNPOPPED CIRCUIT BREAKER PULLED, MASTER ON, AIRCRAFT RETURNED TO BASE. SWITCH REPLACED AND PROPERLY WIRED USING AM 36152 TERMINALS.