Braddism

Ok gentleman, another question. I pulled the glove box out (98 es300) and pluged up a used cd changer to the existing plug. It comes on fine, the discs are being read ok, but I don't get any sound. Two questions, a) is there only 1 plug that goes into the back because I see another little slot on the rear of the changer? b) doe's the unit need reset? Thanks guys.