Industrial Control Wiring Guide PDF filesizes, types and colour of the wiring, to the electrical tests that should be done on the finished equipment. Within BS EN 60204 there are references to other standards, including BS EN 60947, that will give more detail on individual parts or components. BS EN 60947 and the international standard IEC 947 Trailer Wiring Diagram – Lights, Brakes, Routing, Wires Typical Trailer Wiring Diagram and Schematic. These 2 wire diagrams fit the needs of most trailers. The image above shows a single axle trailer, and the next image shows wiring for Tandem Axles. Only the (blue) brake and (white) ground wires are different. Expand the same for additional axles. Use only the needed wires, and ignore the others.