What was found
AFTER TAKEOFF, THE CREW RECEIVED AN APU FIRE WARNING. CREW DISCHARGED APU FIRE BOTTLE & RETURNED. FIRE WARNING DIDN'T CANCEL WHEN FIRE BOTTLE WAS DISCHARGED, SO CREW DECLARED AN EMER & EVACUATED ACFT ON THE RUNWAY. INSPECTION REVEALED NO EVIDENCE OF FIRE IN APU AREA. ACFT REPOSITIONED FOR INVESTIGATION OF FALSE FIRE WARNING. FOUND WIRE SHORTED AT APU LOWER FWD OVERTEMP SWITCH. REPAIRED WIRE. OPERATIONS CHECKED GOOD.