aux input

I added an Aux in jack at the helm, and connected to the back of the Clarion head unit with RCA cables. If the head unit is on FM, AM or Aux then you can hear what's hooked up through this RCA cable no matter what, as long as the volume is higher than zero. So say you set it to an FM station...

I have this input on the side of the cabinet to the left of the main control panel. I plugged my ipod in and it doesnt play. Does anyone know what this is for?