What was found
BRAKE SOURCE LIGHT ILLUMINATED WHILE ARRIVING IN MEMPHIS ... PASSING 10,000 FT. RAN QRH , DECLARED EMERGENCY , LANDED ... DID NOT TAXI . THE BRAKE SOURCE LIGHT REMAINED ON AFTER SELECTING RESERVE BRAKES. NOTE: PILOT DEBRIEF - ALL HYD. PRESSURES WERE NORMAL, ALSO GOT A ANTI-SKID ECIAS MESSAGE. VERIFIED BRAKE ACCUMULATOR PRESSURES WERE WITHIN LIMITS REF 757 AMM 12-15-04-3. VERIFIED INTEGRITY S415 ALTN VALVE SELECT PRESSURE SWITCH REF 757 SSM 32-41-01. REMOVED REPLACED ANTISKID/AUTOBRAKE CONTROL UNIT IAW 757MM 32-42-04-1. ALL OPS CHECKS ARE GOOD.