7 pin RV style plug has a wire that comes DIRECTLY from your trucks battery. Its a Constant source of 12V's.
wire colors may vary.
All you have to do is get a Deep cycle battery, wire the #4 & #1 wires to it. Now it will charge off of the truck when connected. Then wire the Flash kit to the battery. After the flash kit and switch is wired up, you wire up your lights and you're good to go!
I Have done this exact job before in 2 Hours. (warning lights and a Electric jack)