- Small trailers, such as those used to haul motorcycles, are typically light in weight. Larger trailers, such as those used to haul boats, are capable of carrying a higher payload, are wider and must be wired differently--especially if the trailer uses electric trailer brakes.
A trailer that is large in size or width or has a large load capacity will need more marker lamps than will a small trailer. In addition, a heavy trailer is more difficult for an automobile to stop, so these trailers must use additional braking measures, such as electric trailer brakes. Wire such a trailer with a five-way system at a minimum.
Since a trailer that is used to haul light loads (or is physically small in size) typically will require only basic wiring, you may choose to wire it with a four-way system instead.
- In a trailer wiring system, each color represents which light must be wired to that wire, and what function that light performs.
In a four-way system, connect the yellow wire to the left turn signal and stop lamp. The green wire should be connected to the right turn signal and stop lamp. When the brakes are applied, both yellow and green wires are active.
The four way system also utilizes a brown wire and a white wire. Connect the brown wire to the tail lamps, side markers, and license plate light. The white wire serves as a ground wire and is connected to the trailer frame to serve as a ground connection for the trailer.
In a five-way system, the above wiring conventions are used, with an additional blue wire. The blue wire is used to operate trailer brakes or can be used as an auxiliary power connection.
Six- and seven-way trailer wiring systems diverge from the conventions of the four- and five-way systems. In a six-way system, connect the green wire to the right turn signal, and red wire to the left turn signal. Connect the blue wire to the brake signal. Tail lamps should be wired to the brown wire, and black should be wired as an auxiliary power connection. As with the four- and five-way systems, connect the white wire as a ground wire.
Seven-way systems are similar to six-way systems, with the exception that auxiliary power should be connected to the yellow wire. The black wire connects to the vehicle battery.