If you are looking for a few pointers as well, I'd try e-mailing the guys at http://www.classicresto.com/. They were the first to drop a mini into a car and I'm sure they would know for sure.

But with the interference, it sounds like you are not getting constant power. You could try dropping a small regulator between the power connection on the display to see if that would help as opposed to possibly killing a mini in the process.
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