Note: Focaljet and other Ford Focus forums all tell about how you can make your own cable but buying this premade and ready for install for $16 is way less of a headache and probably cheaper than making your own. Best investment period for this project.
Note: You can get these at Autozone, Amazon, Walmart anywhere. You might be able to use a cut up coat hanger but you risk scratching your dash as they don't always play nice and can get stuck. The right tools make the job so much easier.
3.5mm Male to Male Cable (headphone type cable): Radioshack, Walmart, your junk drawer.
Note: Some sellers don't list the name 'Blaupunkt' in the title of the listing so use different combinations to find all the results. Be sure to get one that doesn't have missing pixels as this model has issues with lines of pixels disappearing.