What was found
DIVERTED DUE TO AN APU FIRE INDICATION RECEIVED INFLIGHT. COMPLIED WITH QRH PROCEDURE & APU FIRE INDICATION EXTINGUISHED. AIRCRAFT WAS AT 11,000' AND 260 KTS. [AIRCRAFT LANDED WITHOUT INCIDENT OR FIRE DAMAGE.] UNDER FURTHER INSPECTION FOUND MOUNTS NOT SEATED ON BULKHEAD/FIREWALL. SEALED AS NEEDED IAW BD-100 SPM CHAPT 20-60. INSTALLED NEW DISCHARGE CARTRIDGE INTO A MODIFIED FIRE EXTINGUISHER CONTAINER AND INSTALLED CONTAINER REF 26-21 BD-100 AMM. NO DEFECTS NOTED. INSTALLED 2 REMIANING DISCHARGE CARTRIDGE IN ORIGINAL POSITIONS.