http://www.mustangworld.com/ourpics/fcar/despeeds1.htm should be the same for the mach 1000. i am actually in the process today of doing exactly this. with the same box laid in the back seat and everything. my problem is that my line out converter isnt working right. i hook it up like it says and i get intermittent results. at first it works beautiful then fades out and stays off and all sorts of weird stuff. im gonna play with it more tomorrow and get it to work. i was crossing some wires just tonight after i got home and it seemed like somehow crossing the positive and negative wires gets it to work?
i have no idea, but tomorrow i should have an answer. head to that link as it is fairly informal.