Electric Trailer Brake Wiring Schematic | Free Wiring Diagram Assortment of electric trailer brake wiring schematic. A wiring diagram is a streamlined conventional pictorial representation of an electric circuit. It reveals the parts of the circuit as streamlined forms, as well as the power and signal connections in between the gadgets. Trailer Wiring Diagram – Lights, Brakes, Routing, Wires In the Trailer Wiring Diagram and Connector Application Chart below, use the first 5 pins, and ignore the rest. If your truck has a built-in 7-pin socket, but you only need 5 of the pins. Use the 7-pin connector anyway (see below), and just leave out the last 2 wires.