It’s the gray and green wires near the left gray wire nut. There may be a two-pin connector under the smoke unit (you may have to unscrew the smoke unit to access it). If not, you will have to unsolder the wires from the fan motor to do the lamp test, mentioned above (note polarity) as the wires terminate in the 40-pin socket on the board.
It looks like someone did some repairs as the power wires were spliced/insulated due to a short, pinch or rubbing.
