As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI #2 ENG START SELECTOR, SELECTED TO " GROUND" "VALVE" LIGHT DID NOT APPEAR ON THE SINGLE + BOTH POSITION. AC RETURNED TO THE GATE AND WAS GROUNDED BY MTX. MTX THEN DEFERRED THE RH ENGINE START CONTROL IAW MEL ABX-80-00-2-1 RETURNED AC TO SERVICE ,AND THE AC DEPARTED .