What was found
DURING CRUISE ON TRAINING FLIGHT, THE PILOT SIMULATED AN ENG FIRE BY TESTING AMP SIDE OF THE LT FIRE SYS TO ILLUMINATE THE FIRE WARNING T HANDLE. THE RED LIGHTS ILLUMINATED FOR APPROX ONE SECOND & THEN EXTINGUISHED, DESPITE THE SWITCH STILL BEING DEPRESSED. AFTER SEVERAL SECONDS BOTH PILOTS NOTICED A ELEC BURNING SMELL, THERE WAS NO VISIBLE SIGN OF SMOKE IN COCKPIT. THE PILOT OPENED THE CABIN VENTS IAW CHECKLIST INSTRUCTIONS, THE BURNING SMELL DISSIPATED. THE PILOT DIVERTED BACK & LANDED WITHOUT INCIDENT. TROUBLESHOOTING REVEALED, CHAFED WIRE ON LT ENG FIRE DETECTION SYS. REPAIRED CHAFED WIRE & PERFORMED OPERATIONAL CHECK OF FIRE DETECTION SYS. OPERATIONAL CHECKS WERE NORMAL.