cd changer installation on 99 323i e46
I need help, I just bought a used cd changer for my 99 323i and I found the wires in the trunk and plugged it. The changer is not doing anything and the radio does not appear that it even recognize that there is a cd changer plugged in. is there any steps that I must follow in order for the radio unit to recognize the cd changer? also I found the wires that go to the changer it was to sets, I also noticed that there is a round input right next to where the wires go, is there a third wire that needs to be connected or just the two harnesses.