For the steering wheel controls why don't you use a cheap IR reciever with the PAC SWI-X? I read this thread on MPScar.com and it soundled like it would work. For some reason I thought that this has already been done on a 3S.
http://www.mp3car.com/vbulletin/faq-...your-pc-4.html
Cheap IR reciever
http://cgi.ebay.com/ws/eBayISAPI.dll...MEWA:IT&ih=009
Thanks for answering all my newb questions
