What was found
15 MINS AFTER APU SHUTDOWN APU FIRE CAS MSG CAME ON IN FLIGHT. COULD NOT CANCEL MSG APU FIRE/OVERHEAT TEST NO GOOD. NO INDICATION OF FIRE VISIBLE ON GROUND. VISUALLY INSPECTED APU REAR COMPARTMENT, FOUND APU FIRE LOOP CONNECTOR PLUG TO BE COMPLETELY DISCONNECTED FROM RECEPTACLE. RECONNECTED APU FIRE LOOP CONNECTOR PLUG, PERFORMED APU FIRE DETECTION SYS. OPS TEST IAW MM 26-10-25 PGS 501-504. NO FURTHER DISCREPENCIES NOTED.