What was found
A/C RETURNED TO PLATFORM. DURING ENGINES STARTING, LT GENERATOR LIGHT TURNED ON. DETECTED THAT RT GENERATOR AND APU GENERATOR DID NOT GET THEIR BARS. CROSS FEED SUPPLY OUT OF SERVICE. LT GEN OFF LIGHT TURNED ON. GCU OF APU REPLACED IAW MM 24-20-00 CORRECTING THE FAILURE. BCU REPLACED BUT FAILURE CONTINUED IN CROSS FEED SUPPLY AND LT GENERATOR LIGHT. RT GENERATOR DEFERRED IAW MEL 24-8. DURING OVERNIGHT SERVICE, RELAY R2-33 WIRING WAS REPAIRED IAW WDM 30-27-00. ENGINE, APU GENERATOR AND EXTERNAL POWER WERE TESTED AND RELAY R2-37 REPLACED IAW MM 24-20-06, MM 24-40-00 AND MM 24-20-00 RESPECTIVELY. DEFERRED REPORT CLOSED.