What was found
AIRCRAFT WAS GROUNDED: PILOT DECLARED EMERGENCY ON ACCOUNT OF ELECTRICAL ISSUE. DURING LEVEL CRUISE FLIGHT @ FL 340 RECEIVED CALL OF LIGHT AND LAVS INOP CHECKING STATUS PAGE REVEALED 15 STATUS MESSAGES INCLUDING MAIN DC FEED RPDU 21 AND NUMEROUS CARGO FIRE DETECTION SYSTEMS. MAINTENANCE REMOVED AND REPLACED P300M4 SLOT-12 DC2 CIRCUIT CARD, M2461804 IAW AMM 24-09-09 FOR MAINTENANCE MESSAGE 24-39096. INSTALLATION TEST PASSED. NO FAULTS.