The following trailer brake wiring diagram contains detail illustration of the typical brake applied in trailers. There are 3 brake systems i.e. electrical brake, air brake and vacuum-hydraulic brake. In the electric system the braking system consists of brake controller, stoplight wire, battery, hydraulic connection, master cylinder, power wire, variable resistor (optional), brake wire, ground wire, breakaway switch, battery for breakaway switch, and towing vehicle trailer connection. Please note that actual installation will vary depending on controller system used.