ACFT MADE A PRECAUTIONARY LANDING AFTER GETTING A FIRE WARNING INDICATION IN THE #2 ENG. INITIALLY THE INDICATIONS, BOTH THE FIRE WARNING LIGHT AND BELL, WERE INTERMITTENT; HOWEVER, THEY THEN WENT TO STEADY AND THE CREW SECURED THE ENG AND DISCHARGED BOTH FIRE BOTTLES WITH NO EFFECT. INVESTIGATION REVEALED THAT THERE HAD NOT BEEN A FIRE OR OVER TEMP CONDITION AND THAT THE ENGINE FIRE DETECTION LOOP WAS SHORTED OUT ON BOTH ELEMENTS. CONTAMINANTS WERE FOUND ON THE CONNECTORS AND PINS OF ONE END OF THE LOOP DURING INITIAL INSP. AFTER HANDLING AND SHIPMENT TO THE OPERATOR'S MAINTENANCE FACILITY, THE SHORT DISAPPEARED AND COULD NOT BE DUPLICATED. LOOP MET ALL MANUFACTURERING SPECIFICATIONS AND FUNCTIONED NORMALLY DURING ALL TESTING. CONTAMINANTS APPEARED TO BE ENGINE OIL AND HYDRAULIC FLUID. NO DETERMINATION WAS MADE ABOUT HOW OR WHEN THE CONTAMINANTS WERE INTRODUCED TO THE HERMETICALLY SEALED CONNECTORS.