What was found
PILOT REPORTS "PASSING 5000' ON APPROACH THE L ENGINE FIRE WARNING LIGHT ILLUMINATED AND WENT OUT. THIS REPEATED FOUR TIMES IN THE NEXT 2 MINUTES. THE POWER WAS IMMEDIATELY RETURNED TO IDLE ON THE FIRST OCCURRENCE. THAT CHANGE APPEARED TO HAVE NO EFFECT. MAINTENANCE INSPECTED ENGINE AND FIRE DETECT SYSTEM WIRING AND ELEMENTS. CHECKED RESISTANCE OF LT FIRE DETECTION HOT SECTION, FIREWALL AND GEARBOX ELEMENTS, ALL WITHIN LIMITS. PERFORMED INSULATION RESISTANCE CHECKS WITH NO DEFECTS NOTED. REPLACED LT FIRE DETECTION CONTROL BOX. GROUND TEST AND OPERATIONAL CHECK FLIGHT SATISFACTORY.