my friends got a 98 ram. i pulled out his stock radio and put in a sony cd player. i used the wiring kit from wal mart, all wires are connected, yes even the remote, antenna illumination, all of them... ok so when your listening to the radio, all the speakers work good and sound great, but when you switch over to a cd only the back 2 speakers work.. yea i checked the fade and balance, cant think of what else it could be.

 

1. tripple check your wiring just in case. Don't just look and say "yeah... its hooked up right", really follow through and check.
2. Since you just put in a cd player, look in the manual for troubleshooting with this radio. I have always heard that sony has good customer support, so that is the next step. Give them a call.
3. If the above two don't work, swap out the cd player with a replacement.