Should be a gps intended plug under the tank, front left side (while seated) of the steering head, similar to the Norge. You can buy a plug-in from BMW or Mercedes (think it is a fog light plug) that plugs straight on or do what many do and cut the end off and wire in a more standard plug.
I used this to power my GPS, USB power plug and my auxiliary driving lights in the front.
Someone will have a pic I'm sure but the plug has a green center if I remember.