First, you reference the pinout that you posted to the UK site... which uk site? Do you have the web address? Also, you mentioned that you weren't going to be installing your touch screen into your new car - any interest in selling the cables and power brick that you have?
Finally, the reason for the 8 pin RS232 connector (which I'm sure you know now) is to support the magnetic strip reader and the touch screen at the same time.
Please get back to me - I very much appreciate any help you can provide.