If you have a winch and a car battery to run it w/ in/on your trailer, use this for your break-away battery. My winch battery is charged anytime the truck is running w/ the trailer connected. The break-away switch is a small spring loaded contact held open by a plastic pin. The pin is connected to your truck via a small cable. If things come unhooked, the pin is pulled and power is applied to your brakes. My open trailer I used in 2005/2006 had one, but the one I have now doesn't. Hell the brakes don't work at all now. Man, I gotta get that fixed.