Then most likely its the amp in the stereo. Many of these have taken a crap, including mine. Mine at first was one speaker, then one side, then one on the other side, then the back. Would have been a suedo-quad if I could have gotten them all to do it at the same time.

Some have sent theirs off to a place to have the board replaced. (@$400. Others, which I'm planning on doing, have installed a Jensen marine radio for @$200 that is waterproof, has ipod hookup, and can have a sirius/xm hookup. The only downfall for this setup is the handlebar controls don't work with it, which really doesn't bother me as the unit is sitting there right in front of you. For about the last three years I've just been using my Creative Zen mp3 player with some Sony earbuds, which sounds real nice, but I miss not having the external option. Do a search for Jensen, and several threads will pop up from guys who have already put them in.