Hey dude,
If both lights are out it's probably yellow-gray. Trace it back, it should lead to the coin-door board so you don't have to trace all the way back to the backbox.
J3-8 on the coin door board is the line coming from the power board.
J7-1 should be the line that feeds your start and launch lamps.
If that wire doesnt do it trace down the red-blue and red-gray wires in the same fashion - from the coin door board.