Stereo System Problem (Won’t Play Both Sides At Once)

I’m having a problem with my stereo system. I have it hooked up correctly…But for some reason, When I set it to play A + B sides. It plays only B quietly. When I set it to A, it plays A loud. When I set it to B, It plays B loud. If you don’t understand, I can’t get both sides to play at once.
Answer #1
describe your input and output connections
sounds like you have your wires crossed
Answer #2
What do you mean by that? As in, I have one of the wires in the wrong spots, or the set of wires in the wrong side?
Answer #3
I have one of the wires in the wrong spots, or the set of wires in the wrong side?
it’s possible
Answer #4
I have a feeling I know why..