What was found
SJC FLIGHT NR 2452: NR 1 AC GEN CAUTION LIGHT ILLUMINATED AFTER ENGINE STARTED WITH BOTH PROPELLERS OUT OF FEATHER AND ALL PITOT STATIC SWITCHES ON. AIRCRAFT RETURNED TO GATE. MAINTENANCE SWAPPED NR 1 AND NR 2 AC GEN GCU IAW AMM TASK 24-21-06-000-801 AND 24-21-06-400-801. GROUND RAN A/C. NR 1 AC GEN CAUTION LIGHT REMAINS ILLUMINATED. REINSTALLED GCU'S IN ORIGINAL POSITION IAW TASK 24-21-06-000-801 AND 24-21-06-400-801. REMOVED C/P 24-21 P4-1 AND INSPECTED. CLEANED AND RESECURED. INSPECTED EPCU FOR CURRENT FAULTS. FAULT CODE 27 WAS FOUND. REMOVED AND REPLACED NR 1 AC GEN IAW MTC 624201. PERFORMED OPS TEST OF A/C SYSTEM IAW AMM TASK 24-24-00-701-801L. OPS CHECK GOOD. NO FURTHER DEFECTS NOTED. A/C GE