As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING DESCENT INTO ILN, APU FIRE INDICATION. APU WAS NOT OPERATING AT THE TIME. COMPLETED APU FIRE EMERGENCY CHECKLIST INCLUDING DISCHARGE OF FIRE BOTTLES. LIGHT WENT OUT AFTER APPROX 3 MINUTES. LIGHT RE-ILLUMINATED APPROX 5 MINUTES LATER FOR APPROX 30 SECONDS. FOUND WIRE PULLED OUT OF PLUG P1-278. REPLACED PLUG P1-278, TESTED FIRE LOOP SYSTEM PER DC9 MM 26-10-02-2 WITH APU RUNNING AND WITH APU SHUT OFF. NO DEFECTS NOTED.