I got my speakers installed by a shop and this happened with my rear passenger side speaker - the more power you put to it, the less it would play. they fixed the problem - but I am pretty sure their explanation made it sound as if the positives and negatives for different speakers were mismatched. ie. the + wire for the front left speaker was paired with the - wire for the right rear speaker, and then both were run to the right rear, so weird things happened. your wires might be crossed somewhere, but for the speakers to play at all they are most definitely plugged in so that can't be the problem.

1995 Eagle Talon ESi