Pac C2R-CHY is what you need.
If you want to keep the steering wheel control you need:
SWI-CAN AND one of the following (depends on brand of radio
you are using):
That will get you started. Eventually you may want to upgrade
the speakers. At that point it would be recommended to wire
the radio directly to your replacement speakers or get an amp
Mods (2005 C): Stereo only, PAC SNI, Peripheral CHYX, XM Commander, AudioControl four.1, MTX TA5604, MTX TA5601, Polk MMC6500, Polk MMC690, JL CS212R-W0 (2013 C): None..........yet