I should think your truck would already be 12 volt.
Some of the best advice has already been given--read everything you can and learn as much as you can before diving in too deep. I don't know the extent of your mechanical abilities-mine are rather limited-but it helps to have as much background information as possible before tearing into anything. If you're willing to learn as you go, then go for it!
It also sometimes helps to do little things first, one at a time. That way you can keep driving it in between, which helps keep your enthusiasm up. A lot of projects never get finished because they get torn all apart, and then the owner gets discouraged and loses interest.
