Photo of trailer being connected to tow vehicle

Connecting Your Trailer to Your Tow Vehicle

Tow vehicles and trailers must be compatible with hitching, braking, and wiring systems to ensure safety.

Hitching Systems

The trailer towing industry has developed a classification system that differentiates hitches according to the amount of weight they can tow. This system addresses tongue weight and total weight. Keep in mind that within each classification are numerous hitches made by a variety of manufacturers.

The three most common types of hitches are the weight-carrying hitch, the weight-distributing (or load equalizer) hitch, and the fifth-wheel hitch, or gooseneck. Weight-carrying hitches are designed to carry all of the trailer’s tongue weight. Weight-distributing hitches are used with a receiver hitch and special parts that distribute the tongue weight among all tow vehicle and trailer axles. Fifth-wheel hitches are designed for mounting the trailer connection point in the middle of the truck bed.

Illustration of fifth-wheel hitch
fifth-wheel hitches

When purchasing a hitch, use the recommendations of the manufacturer of the tow vehicle and trailer based on the type and weight of the trailer. Make sure the hitch has provisions for the connection of safety chains, which are required by most states. When connected, safety chains should have some slack to permit sharp turns but should not drag on the road. In addition, they should cross under the trailer tongue to help prevent the tongue from dropping to the road in the event the trailer separates from the tow vehicle.

Illustration of safety chain
safety chains

Braking Systems

The selection of a brake system also will depend on your tow vehicle and the type and fully loaded weight of your trailer. For a trailer with a loaded weight of more than 1,500 pounds, many states require a separate braking system and a breakaway switch, located on the tongue of the trailer, to activate the trailer brakes in the event the trailer separates from the tow vehicle. There are two basic types of brake systems designed to activate the brakes on a trailer:

  • Electronically controlled brakes usually provide automatic and manual control for trailer brakes. They require that the tow vehicle be equipped with a controlling device and additional wiring for electrical power. These brakes typically have a control box installed within reach of the driver and can be manually or automatically applied. The control box may require adjustment or “tuning in” for variations in trailer load. 
  • Surge brakes are independent hydraulic brakes activated by a master cylinder at the junction of the hitch and trailer tongue. These brakes are not controlled by the hydraulic fluid in the brake system of the tow vehicle. Note: The hydraulic system of the tow vehicle should never be directly connected to the hydraulic system of the trailer. These systems are self-compensating and do not require adjustment for variation in trailer load.

Follow the tow vehicle manufacturer’s recommendations for brake selection. Some states require braking systems on all axles of the trailer. So, check your state’s requirements by contacting the motor vehicle administration.

Wiring Systems

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.

Illustration of connector

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.

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