12V outlet

[oldkid]

Unless you plan to install under the seat or another protected area, you will need a water proof type. I used a marine type that was made to be used outside. Nothing to rust and has a plug in seal when not needed. I did want mine to be active all the time so I could plug in my Battery Tender so I hooked directly to the battery with a fuse near the connection.
I guess if I wanted it to only be active with the bike running, I would choose the power that runs the horn. It's usually a large enough wire, and should have power with switch on. The horn button usually only makes ground connection, but you should test to make sure.