Wiring Instructions for Horse Trailers

Horse trailers are required to have at least brake lights, running lights and turn lights. Since most horse trailers do not have a power source, they must tap into the tow vehicle's wiring. Hooking up a horse trailer requires a T-One connector, an external wiring box which is pre-wired to a 4-pole flat connector. This horse trailer connector comes in several different forms, one of which should fit into the connectors of your personal vehicle. Consult your owner's manual to locate the correct T-one for your vehicle.

  1. Installing the Components

    • Determine which kind of trailer plug shape your trailer uses. The simplest way to tell is by shape; the trailer will either have a round trailer connector or a square trailer connector. You need a matching receptacle on your vehicle. Some personal trucks and SUVs come already equipped with a tow ball on the back bumper. If your vehicle does not have one, take it to an auto shop to have it welded on. It should be mounted on your bumper for a bumper pull trailer or mounted in the bed of your truck for a gooseneck trailer.

      Install the T-one connector for your vehicle. The T-one wiring connector plugs into your vehicle's existing wiring system. Locate the appropriate wiring by removing a tail light and following the wires backwards from the light. Unplug the wiring on your vehicle at the connectors leading to the rear lights, and plug in the T-one connector. This means that you'll have tail lights on your trailer instead of your vehicle.

      Most horse trailers operate a separate braking system controlled by an electronic brake controller. Purchase a brake control box and have the controller professionally installed so that your electronic trailer brakes function correctly. Many trailer companies install these controllers for a minimum fee.

    Connecting the Components

    • After you have installed the T-one connector and your trailer plugs, begin attaching the wires to their sister parts. Begin by locating the ground wire--the white wire on the connector. Attach the ground wire to a good ground, such as a bolt or screw running through the metal bumper or frame. A properly attached ground line will keep your system from shorting out and becoming ineffective. The wire can be attached either by electric drill or by wrapping the wire around the screw or bolt.

      Once the ground wire is attached, determine which wires serve what function. The 6-way connector on your trailer should have wires for tail lights, electric brakes, left turn light, right turn light and a 12-volt hot lead. To determine which wire is which, turn on each signal and connect a 12-volt tester to the connector to test the wires. Attach the yellow wire on the connector to the left turn signal light. You can use scotch locks to quickly make the connection at the wires. Now attach the green wire to the right turn signal light wiring. The brown wire is for your tail lights. The blue wire is for your electric trailer brakes.

      Before hauling anywhere, always visually check your trailer lights and your brake system. Take a moment to test that brake lights are working as well as both turning signals. Have someone stand behind the trailer while you turn lights on and off, or turn on your hazard lights and go to the rear of the trailer; if both signals are flashing, you have a good connection and are ready to haul.