What was found
ENROUTE, WITH ENGINE ANTI-ICE ON, THE LT ENGINE FIRE LIGHT ILLUMINATED. FOLLOWING AFM EMERGENCY PROCEDURES, THE CREW REDUCE LT ENGINE TO IDLE POSITION AND THE LT FIRE LIGHT WENT OUT. CREW DECLARED EMERGENCY AND DIVERTED BACK TO DEPARTURE. ACFT LANDED WITHOUT INCIDENT. MX ON SITE RAN ACFT AND WERE ABLE TO DUPLICATE DISCREPANCY. THEY FOUND THE FIRE SENSOR ROUTED IMPROPERLY AND IT WAS TOUCHING THE BLEED VALVE. THE FIRE SENSOR WAS ROUTED IAW THE MM 26-11-01. A GROUND RUN UP WAS PERFORMED SATISFACTORILY WITH NO WARNING INDICATIONS AND THE ACFT WAS RETURNED TO SERVICE.