So I've got this 01 Ram 1500 Quad Cab with a stock stereo that finally died. 4 speakers and 2 tweeters. My wife gave me a Sony HD radio for X-mas. There's this blue and black wire that clips to the back (outside exterior - don't know how else to describe it) of the stock radio. The other wires in the harness match the harness that came with the stereo. So what's the blue and black wire that clip to the back of the stock stereo for?
Also, without hooking up this blue and black wire, the stereo works but I have no sound. I've made sure the connections are secure where I connected the wires and the "ATT" feature on the stereo is off. The balance is centered, etc. Any thoughts, especially on the blue and black wire?