I installed a USB plug onto my BB today. I mounted it using two of the fairing push in plugs underneath the tacho into the plastic dash surround. USB seems to be the standard these days so I went with that. I'm only looking to charge my phone out of it while riding. Others will go for the cigarette plug. I got the plug from Burns Moto in the USA.

Installation was easy, connecting straight to the battery using electrical conduit from the plug to the left of the steering stem ensuring enough length to allow full lock of the handlebars either way. Then beside the tank underneath the plastic tank surround straight to the battery. Very easy installation that can be done yourself.

BurnsMoto - Motorcycle, ATV, Boat, RV - USB Weatherproof Power Socket - USB Charger with optional SAE to USB