What was found
(CAN) WHILE PICKING UP A WATER LOAD THE GROUND POWER UNIT - 2 FIRE WARNING LIGHT STARTED TO FLICKER AND THEN STAYED ON STEADY WITH THE WARNING BELL. FOLLOWING PROCEDURES THE CREW SHUT DOWN THE RT ENGINE AND DISCHARGED FIRE BOTTLE INTO THE NACELLE PROTECTED AREA. AIRCRAFT LANDED WITHOUT INCIDENT. NO SIGN OF FIRE IN GPU-2 AREA. APPEARS TO HAVE BEEN A FALSE INDICATION. SYSTEM WIRING CHECKED BY MAINTENANCE - UNABLE TO DUPLICATE FIRE WARNING.