Take the cover off the starter motor which has the accessory socket on. Then plug it in so power goes to the GPS and the socket. Easier to see and work out when the cover is off and the plug is taken off the back of the socket.
Or, if you have the beak socket, same idea but don't bother taking off the starter cover.
Done it once or twice. One thing that can happen is for the GPS lead to corrode if the power is live all the time, as it will on the 1150. I used to disconnect the plug during periods when I wasn't going to ride the bike for a while. Not all people have the problem though
Once the starter cover is off the longest part is making sure you don't interfere with the throttle cable with the cable's routing. If you use the beak socket, which is just the left boot one but in parallel then it's even easier, honest!