What was found
AIRCRAFT RETURNED TO PLATFORM, AC CROSS TIE AND APU RT BUSS LIGHTS TURNED ON. BCU WAS REPLACED IAW MM 24-20-00 AND AC CROSS TIE LIGHT TURNED OFF, BUT RT BUSS LIGHT CONTINUED ON. RT BUSS LIGHT WAS DEFERRED BY MEL 24-1-1 AND AIRCRAFT WAS DISPATCHED. AFTER, AIRCRAFT RETURNED OF FLIGHT DUE TO THE SAME FAILURE AND CAPTAIN PERFORMED ABNORMAL PROCEDURE. DURING MAINTENANCE CHECK, THE RT AUX POWER RELAY WAS DETECTED CLOGGED. THE RELAY WAS REPLACED IAW MM 24-20-06, TESTED CORRECT.