I have a 04 Freestar with a factory rear DVD system, but the head unit was replaced with an aftermarket (Kenwood) which we can not stand. It belongs in some 19 year olds Honda Civic. I'd like to put a Ford head unit back in there but I'm not sure how to tell which one it would need. Is there any way to tell? Also I see on ebay some nonsense about needing to have it programmed to the vehicle, what's that all about?