Does it have the CD changer as part of the head unit, or is it placed separately, like in the console or under the seat?
I have one (factory) in the console. I was able to find the output wires of the changer, then wire in a headphone jack to feed in my mp3 player.
If you have one of the ones that is combined in the head unit, you will either need to be a very good electronic tinkerer, or buy an adaptor. I'll look for the adaptor I'm thinking of if that's the case, so if you respond, I'll be able to give you a link.
Hope you reply, so we can get your mp3 player in your truck...I sure enjoy mine!