Rather than tie into the electric system that is designed specifically for the bike, run a hot wire and ground right to the battery for the plug you want to put in. Just put a small switch on it so it can be turned off and on as you need it. that way you aren't cutting into oem system and causing some issues down the road.
Just one opinion. I would rather put a small block that could be switched and tie all my extras on and be able to use it with the key off. Just don't drain the battery with extended use.