B25 speaker jack

[Retrorod]

I have a question on how to wire a 1/4" speaker jack to a B25. Someone previously cut the xlr style plug. I am left with 4 wires. Which 2 wires would hook up to a mono jack? The aux speaker jack is intact.
Thanks, I am struggling with thinking this through. If I remember correctly there are 2 black, 1 red and 1 green wires....