there isn't one, you have to add one, Ford has a kit called trip tunes,
part #6R3Z-19A464-AA that you can purchase and install, this will allow you to connect your Ipod
and listen to your tunes thru the factory speakers, also you'll be able to control the volume, but you will not be able to control the functions of your Ipod with the radio, also there are
a number of aftermarket kits that you can buy that allow you to control everything thru the radio but they are alot more then the $50.00 that Ford wants.
The stock MP3 designation is for the type of disc it will play. You can burn lots of CD's (like 7) onto a single CD in MP3 format. That is why they say it is MP3, not because of the jack. You have to add the jack to the back. I'm actually searching for that right now. I run all 6 loaded with MP3 and it gives me plenty of driving tunes.