What was found
AFTER ENGINE SHUTDOWN, POWER WAS ON APU FOR 1 MINUTE. WHEN EXTERNAL POWER WAS CONNECTED ALL POWER WAS LOST. SLIGHT ELECTRICAL ODOR IN THE COCKPIT, POWER COULD NOT BE RESTORED WITH POWER RESTART. THE AIRCRAFT WAS GROUNDED. MAINTENANCE ACCOMPLISHED CABIN ODOR TROUBLESHOOTING IAW JC 26L00021001, THE SOURCE WAS DETERMINED TO BE A FAILED CONTACTOR. REPLACED THE CONTACTOR IAW AMM 24-51-55, AND PERFORMED A SATISFACTORY OPERATIONAL CHECK.