What was found
(CAN) DURING TAKEOFF, ODOR NOTICED IN COCKPIT. FLIGHT CONTINUED. SMOKE AND SPARKS NOTICED FROM BEHIND AREA WHERE LANDING LIGHT SWITCH IS LOCATED. MASTER TUNRED OFF AND AC RETURNED TO FIELD. DURING THIS TIME, A FIRE HAD STARTED RIGHT BEHIND THE LANDING LIGHT SWITCH AND WAS EXTINGUISHED USING THE ONBOARD FIRE EXTINGUISHER. AC LANDED WITHOUT FURTHER INCIDENT. UPON INVESTIGATION, FOUND WIRES FROM BEHIND LANDING LIGHT HAD FALLEN OFF DUE TO LANDING LIGHT SWITCH OVER HEATING AND TERMINALS FROM THE SWITCH FALLING OFF. THIS ALLOWED THE SUPPLY WIRE FOR THE LANDING LIGHT SWITCH TO CONTACT GROUND AND START ARCING WHICH STARTED THE FIRE. THE CIRCUIT BREAKER WAS FOUND IN THE CLOSED POSITION INDICATING IT DID NOT OPEN DURING THE ARCING. (TC NR 20071002003)