Don't know the part number, but here it is on ebay for sale:
http://cgi.ebay.de/Kabelbaum-Navi-fu...QQcmdZViewItem

This plugs into nav (purple + blue) and into video module (white)

The longer black & white plugs then need to be joined to power+ground+speed pulse, all available at the radio module behind the video module

You then only need to run one wire to the reverse light wire on the right hand wheel arch to pick up the reverse signal.