I have a '98 GSR w/ the stock radio and I was trying to hook up an MP3 player by using an adapter in the CD changer port in the back. I got it all hooked up but the radio isn't letting me use the changer button as the source like you are supposed to be able to do. Have I done something wrong? I reset the stereo by disconnecting the battery but then it still works the same. No CD changer. Can anyone help?