I've just tried driving around with all three options selected (L+R, L only, & R only). My music does mute so I know the nav is taking, but there is still no sound. I've read somewhere it might be an amp issue & that I'll have to hook the front channel to the rear in the wire harness. I'm not sure if this was done by my installer or not. I guess I'll mention it to him & see what he says. If that is what is happening would I still get sound from my other sources through all speakers like I currently am? Thanks for the help!