As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
TRIED TO SWITCH TO GROUND POWER AFTER BLOCKIN, THE FIRE BELL SOUNDED FOR 10 SECONDS. NO FIRE LIGHTS ILLUMINATED. NO OTHER INDICATIONS OF FIRE OR ANY OTHER MALFUNCTION. STARTED THE APU AND SHUTDOWN THE LEFT ENGINE. FIRE DETECTION SYSTEM OPS CHECKED NORMAL IAW MM 26-11-00-5.