What was found
(CAN) AIRCRAFT UNDERWENT A CHANGE OF THE LT ENGINE. GROUND RUNS WERE MADE, ALL APPEARED NORMAL. AIRCRAFT WENT FLYING ON A TRIP FROM YVR TO SER. SHORTLY AFTER TAKEOFF, THE LT ENGINE FIRE WARNING LIGHT ILLUMINATED. THE CREW PERFORMED A SHUTDOWN AND DISCHARGED THE FIRE BOTTLE. THE AIRCRAFT RETURNED TO YVR AND LANDING WAS UNEVENTFUL. MAINTENANCE INVESTIGATION REVEALED ONE OF THE FIRE PROBES WAS POSITIONED TOO CLOSE TO A LINE THUS PROVIDING A GROUND WHEN SUBJECTED TO THE VIBRATIONS OF FLIGHT. PROBLEM CORRECTED BY REPOSITIONING PROBE AND PROTECTION BOOT. FIRE BOTTLE SERVICED.