If you plan to add accessories later on I suggest something like this so you don't clutter up your battery terminals with a mess of wires:
Motorcycle Power Relay and Distribution Block | Canyon Chasers Motorcycle Sport Touring
I did that (minus the easy splices, yuck), but wired in the 12v outlet in front of the relay (hotwired for easy access to put on battery tender). I have never left anything plugged in on accident.
If you don't want to add a power distribution block and don't want to hot wire it you could run your positive wire to the headlight. Use the left one as it is always on (unless you have dual headlight mod, then it doesdnt matter). Look for the black wire with green stripe.
Splice into it and run the positive cable of the 12v socket to it. Also, wire in a 5 or 7.5 amp fuse (could be done to negative, but doing it on positive keeps it uniform to the rest of the bike). Run negative to negative battery terminal.
You could run the positive wire of the 12v outlet to any positive switched wire on the bike so long as the gauge of the wire is thick enough to supply power to the accessory AND component which you are piggybacking of of. Use a multimeter to find these positive wires.
Here's mine. (Ignore dirty bike from rain. And tools on floor from getting new tires put on)
Edit:I agree with fizzer6 about not wanting to lose your lights and that it's better to wire into toggle switch, but others have done it with success. Just dont plug anything that demands much power.
