If you want to fit a GPS - Tom Tom Rider or Garmin, all you need is this cable. Plugs into the BMW canbus wiring loom and provides power to your GPS.
I found all sorts of conflicting and confusing info about how to connect a GPS in the forums.
I connected my Garmin (Nuvi) to the BMW GPS outlet and, it triggers the Garmin on but, it does not charge the unit(?). Should it? If not, I assume my options are direct to the battery or direct to the accessory outlet.