What was found
(CAN) RIGHT NON ESSENTIAL BUSS SWITCH LIGHT ILLUMINATED AS THE CREW LINED UP FOR TAKEOFF. THEY RETURNED TO FLIGHT SUPPORT`S RAMP AND SHUTDOWN THE ACFT. A VERY STRONG ELECTRICAL BURNING ODOR WAS ENCOUNTERED AS THEY DISCONNECTED BATTERIES. CONDUCTED RECTIFYING MAINTENANCE AND NOTED THE ROOT CAUSE OF THE DEFECT WAS THE UNSERVICEABLE INVERTER. THEY DID THE FOLLOWING: REPLACED UPPER MAIN BATTERY, SN 40291769 WITH NEW, SN 40438004, PN RG 380E/40L. REPLACED INVERTER PN 2D1200-1A-1011, SN GB001088 WITH REPAIRED UNIT SN GB001485. REPLACED REMOTE CONTROL CIRCUIT BREAKER, PN SM600BA75N1 AND RT NON ESSENTIAL BUS 80 AMP FUSE PN 100 FU01-080 WITH NEW. SYSTEM FUNCTION TESTED GOOD AND NO BURNING ODOR DETECTED. THE ACFT WAS RETURNED TO SERVICE.