It's a proprietary connector, a little square gray plug. You plug in an aftermarket adapter, available here:
CHRY02-AUX | TSS-Radio
...and in a few minutes you're good to go. The audio from the iPod or other external device is input to the adapter with a stereo to RCA Y-cable and to play it, you switch to the CD changer function on the head unit. It displays CD1-Track1 constantly, but that's not really a big issue.
I've had mine set up this way forever and it works great!