Electrical wiring a trailer is made easier with the Tow Doctor. Electrical diagrams and wiring - 4 Wheel and Offroad Magazine ...

This requires a wire from the controller to the trailer brake. (This is why some connectors have as many as seven pins, to make provisions for the multiple circuits.) Use 12-ga. wire for this circuit.

Mitchell 1, a Snap-on company, has added color air brake diagrams to its June update of Tractor-Trailer.net, its comprehensive web-based truck repair manual system.