No wire... In all cases that i am aware of this is something that you have to add to your OEM stereo. This isnt a hidden feature, you will need to buy a wire and then plug it in to the back of the "radio". I don't know the config with a NAV unit but it will not be on the back of the CD or tape player. I am assuming this might also be the cases with the NAV unit so you might need to hook it up in the trunk as that is the location of the computer.

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91 318is x2
97 318ti
03 3.0 X5