There are quite a few people who are adding 12Volt (cigarette lighter type) accessory plugs to their atvs.
I just came across the following plug which is both a 12 (cigarette lighter type) and a 5V (USB type) plug in ONE! Likewise, it can be handlebar mounted which makes installation even easier. With this, you can operate just about any 12 or 5 volt accessory that you want to. Very neat!