As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(AIR TURNBACK) DURING FLIGHT, 5 MINUTES AFTER APU SHUT DOWN FIRE WARNING LIGHT ILLUMINATED. PERFORMED APU FIRE PROCEDURE AND FIRED BOTTLE. WARNING LIGHT REMAINED ILLUMINATED AND HAD INTERMITTENT FIRE BELL. RETURNED TO MSY. FOUND CONNECTOR D4834 CORRODED/SHORTED. REMOVED AND REPLACED CONNECTOR & HARNESS.