What was found
(CAN) PILOT REPORTED ENG ADPT HEAT 1 CAUTION LIGHT ILLUMINATED AND CIRCUIT BREAKER TRIPPED IN FLIGHT, AIR TURN BACK WAS PERFORMED. MAINTENANCE DISCONNECTED CONNECTOR 9811-P350 AND MEASURED PINS K AND L, WHICH MEASURED 2000 (OHMS) AND 11.4 (OHMS) RESPECTIVELY. CONNECTOR PL1 AT THE ENGINE INTAKE DISCONNECTED AND PINS A-B MEASURED 11.3. WIRING BETWEEN P350 AND PL1 CHECKED ALL OK. FOUND CONTAMINATION IN CONNECTOR PL1. CONNECTOR CLEANED AND PIN K MEASURED AGAIN AND FOUND SATISFACTORY (11.3 OHMS). CARRIED OUT OPERATIONAL CHECK OF THE ENGINE INTAKE ADAPTER HEATER, IAW AIRCRAFT MAINTENANCE MANUAL. TESTED OK. AIRCRAFT RETURNED TO SERVICE. (TC# 20180618002)