Federal law requires trailers to have taillights, brake lights, side marker lights, turn signals, and side and rear reflectors. Some trailers also have backup lights. To provide power to these lights, a four-way (or more) connector is hooked into the tow vehicle’s electrical system. Many tow vehicle manufacturers offer a 7-way connector that may include an electric brake signal, power supply, and backup lights, in addition to the typical four functions. Note: You must ensure that the signals on the electrical connector of the tow vehicle match the electrical connector of the trailer.
Because the wiring systems of many tow vehicles use separate wires for turn signals and stop lights, you may need to purchase a taillight converter. This converter will combine these wires so that they can be connected to the trailer lighting system. Most factory-installed towing packages include a trailer wire harness that will perform this function if required. If you tow more than one type of trailer, you also may need to purchase an adapter to accommodate differences in the wiring systems.