I have an AVIC-D1 and I tried plugging my MP3 Player into the "audio input" RCA connectors in the back of the unit, but I get nothing on the radio. When I go to the source menu it doesn't seem to detect anything... I can't touch on the AV or AUX input in the source menu. Am I doing something wrong?

you arent suppose to hear it through your radio tuner, you are supposed to hear it through your av source. Try turning the source av on, and then switching to that source.