Connecting MP3 player to Audio 20

Can someone tell me what cables (part numbers ?) I'll need to connect my MP3 player (Creative Labs) to the Audio 20 unit in a 2005 C180. I don't have, or want a CD changer.
I'm guessing that I'll need a cable to plug in to the back of the Audio 20 unit (Aux or CD changer slot ?) and that will have an earphone type plug at the other end to plug in to the MP3 player.
Rgds Aidan Sherwin
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