What was found
ON DESCENT THROUGH 12000FT, AFT CARGO FIRE WARN CAME ON. THE LIGHT WENT OUT BEFORE A CHECKLIST WAS STARTED... MAYBE 10 SEC. UPON TOUCHDOWN ON RWY LIGHT AND WARNING CAME ON AGAIN. QRC & QRH WERE RAN, HALON WAS DISCHARGED INTO AFT CARGO. THE CREW ADVISED ATC AND THE PORT FIRE DEPARTMENT RESPONDED ON THE TAXIWAY AND VERIFIED NO FIRE PRESENT. GROUNDED - YES. ACCOMPLISHED AFT CARGO ELECTRONICS UNIT (CEU) BITE TEST, NO FAULT FOUND. PRECAUTIONARY REMOVED AND REPLACED AFT CARGO ELECTRONICS UNIT (CEU) AND ALL SIX AFT SIX CARGO SMOKE DETECTORS. REF AMM 26-16-02/401. ACCOMPLISHED CARGO ELECTRONICS UNIT INSTALLATION TEST PER AMM 26-16-02-710-801 AND CARGO SMOKE DETECTION OPERATIONAL TEST PER AMM 26-16-00-70-801. TEST PASSED. REF TASK CARDS 26-360-00 FOR REPLACEMENT OF BOTH CARGO FIRE BOTTLES, OPS AND LEAK CHECKS GOOD.