Hmm, maybe the sound plays through the antenna. I installed 2 of them and both played loud and clear so I can't imagine what you hooked up wrong as each connector is unique shape/size. The fiber has nothing to do with sound, neither does C1 (that's for the CD changer +/- power). The C2 connector is for canbus low/high and fiber wake-up so that has nothing to do with sound. Connector A doesn't, it's mostly power. So your culprit must be connector B, front/rear/left/right speakers if it's a connector issue. It could be that while playing with it you put it on mute, you didn't turn the volume up, you didn't connect the antenna, or it's broken....