How Do Trailer Lights Work?
Mounting
A trailer light can be mounted in many different fashions depending on the model, but the most common type simply mounts to the trailer via one or two bolts with a nut on each end. Manufactured trailers will have provisions and a specified spot for the trailer lights, but custom trailers must be outfitted with custom mounts that work with the style trailer light you wish to use. Also, check the local ordinances to see if trailer lights in your area are required to be mounted in a certain fashion, such as so many feet apart or at a specific height off the ground. Also, ensure that the light is waterproof if it will be going on a boat trailer, because when the boat is launched the trailer lights many times get wet or completely submerged.
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Wiring
Each trailer light is wired directly into the corresponding side of the vehicle’s light wiring. In other words, the left turn, stop, and tail trailer light will be wired into the stop, turn, and tail electronics of the left tail light on the tow vehicle, and the same for the right side. For this reason, if there is something wrong with the tail wiring on the vehicle, the trailer lights will not work, either. If there is only a bulb out in the light assembly on the vehicle, the signals on the trailer light will still operate correctly in most cases. The trailer wiring is often set inside a plastic loom and routed either inside or very close to the frame of the trailer to avoid damage from pinches or road debris. It is always recommended to use 14 gauge or above wiring for the trailer lights, especially if the trailer is over 10 feet long. A thicker wire will create less resistance over a long distance.
Connectors
Of course, the trailer wiring is not attached directly to the electronics of the tow vehicle, or the trailer would be stuck on the hitch. It is separated by a connector that can be attached and removed quickly. The two most common types are a pigtail connector, which is a round hub that is usually attached to the hitch itself and has a cover on it for when not towing, and a 4-way flat connector, which disconnects just as easily, but is usually free-hanging or put into the trunk or hatch of the vehicle when the trailer is not in use. Both connectors provide the same function, and it is almost purely a matter of taste as to which one is chosen. The pigtail type connectors seem to be more prone to failure, but they do mount well and are easy to use.
