This is funny, two almost identical questions on the same night.
Go to your dealer and get a 3 prong pigtail. It plugs right into a spare plug on the harness under your seat. Also get the metal tabs and female plugs to go with it. I just wired my Deuce last Sunday for the GPS power.
Sorry, don't have the part numbers handy at the moment, but that's the easiest way to do it.
I bought a second auto power cord, cut the end off that plugs into a cig lighter, snaked the wire from the handlebar,under the tank, to the battery area, soldered the new male spade connector on to the wire, and plugged it into the harness. The black ground wire went right to the same bracket that the main ground wire from the battery bolts to.
It took me about 30 minutes to do. Using the accessory harness from the dealer will give you three power sources and requires no cutting of the factory wiring.
Decided to brave the downpour and go out to the garage and get the part number for ya.
'ACCESSORY ADAPTER HARNESS KIT' PART # 70270-04
Make sure to ask the parts guy for the matching terminal housings and spades for the harness.