- Typically, wires that connect to the tow vehicle only carry the positive voltage from the battery. The energy for the trailer lights is transferred through a box known as a "converter." The lights are controlled by switches inside the vehicle.
A wiring diagram on etrailer.com shows that various electrical hook-ups are available for power transfer from the tow vehicle to the trailer's lighting system. The connectors, which range from four prongs (basic hook-up) to seven prongs, power tail lamps, turn signals, running lamps and trailer brakes. - A bad ground on a trailer can cause the lights to malfunction.The white wire on the trailer end of the plug is the ground. It is attached directly to the trailer frame in most cases. If no light is working, the cause may be a faulty ground wire.
Alan Glos of duckworksmagazine.com states that rust or corrosion around the ground connections is a common cause of a trailer light not working. Light fixtures, which are bolted to the trailer frame, can rust and lose contact with the frame and create a bad ground. - RV lighting fixtures are most likely to corrode before the wiring gets damaged. RV wiring systems have better protection from the elements because they are enclosed within the body shell of the trailer. RV lighting fixtures can be purchased from retailers or from the RV manufacturer.
- Duckworksmagazine.com's Alan Glos states that utility and boat trailers are constantly exposed to the elements. And if the lights are on a boat trailer, they are exposed to salt or fresh water when the boat is being launched. Therefore, the wiring is subject to chafing and the connectors are subject to corrosion.
- The lights on the trailer may make the difference between a smooth trip or one which can end badly for the driver of the tow vehicle or another motorist. All wiring and the fixtures must be examined by the tow vehicle driver before and after the trip to ensure they are functioning properly at all times.
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