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How to Wire Your Trailer

Wiring your vehicle and trailer for correct towing operation ensures that you stay legal and safe. Sometimes a simple T-connector is all that is needed to operate trailer lights, and a brake controller to utilize the trailer braking system.

Most trucks, vans, SUVs and RVs made since the mid-1990s include factory-installed trailer lighting connectors and ready-made plugs in the cabin for a trailer brake controller.

If your vehicle is so equipped, setting up your trailer electronics is easy. However, even if your vehicle isn't currently wired, installing a wire connector to prepare for towing is simple.

What Connectors Are There and What Are Trailer Wiring Codes

The format shown to the left is the standard wiring format found on most vehicles and trailer wiring kits. If your trailer needs wiring, your best solution is to purchase a light kit that includes wires.

How to Wire Your Towing Vehicle

If your vehicle came from the factory with a towing or camping package, you may already have a vehicle side 4-way flat or 7-way RV blade connector already installed. The 7-way connectors are always in the vicinity of the center of your rear bumper, mounted on a tab or mounted into the bumper itself. Sometimes, 4-way flat connectors are tucked up under the rear of the vehicle. Your vehicle owner’s manual should tell you how to determine if a connector is already installed.

If your vehicle did not come with a factory installed wiring harness, your vehicle may have wiring plugs in place to help you install trailer wiring. Consult the diagram below to see common locations for wiring plugs.

Read your owner’s manual and check your vehicle thoroughly before cutting or tapping into any wires on your vehicle.

How to Connect the Wiring Harness

A wiring harness exists for most vehicles. They range from a T-connector harness (pictured left) that plugs into a factory connection, to a universal harness that must be spliced into the factory wiring.

Many newer vehicles have a connection at the rear of the vehicle. The installation is as easy as unplugging the connection and inserting the T-connector in between the two plugs.

An older vehicle’s existing wiring harness may need to be spliced to install a towing connector. Luckily, most of the wiring you need connects to your vehicle’s tail lights. The exception is the wiring for a brake controller.

If you want 5, 6 or 7-way functions then you need to cut and splice into the wiring. For trailer brake operation please see the electric brakes.

Some vehicles may also require a taillight converter. This converter adapts separate turn and stop lights to standard trailer taillight wiring on import and domestic vehicles.

Trailer wiring color code diagram

1. 4-WAY FLAT

Most lighting kits use the common 4-way flat connector with three male ends and one female end. The connector is designed so that you cannot connect the plug backwards. This connector is mirrored on the vehicle side.

  • Turn Signals
  • Brake Lights
  • Tail Lights
  • Ground

2. 5-WAY FLAT

If your trailer includes backup lights, you can still use a standard wiring kit, but most vehicles that are wired for towing do not include a 5-way flat connection. You may need an adapter or to install extra wiring in your vehicle to support the extra light.

  • Turn Signals
  • Brakes Lights
  • Tail Lights
  • Backup Lights
  • Ground

3. 6-WAY POLE

If your trailer includes back up lights and electric brakes, but is not wired for auxiliary power, then a 6-connect can be used.

  • Turn Signals
  • Brake Lights
  • Tail Lights
  • Backup Light
  • Electric Brakes
  • Ground

4. 7-BLADE RV

If your trailer includes back up lights, electric brakes and auxiliary power, then a 7-way connection is needed. The most common style today is the 7-Blade RV style which uses flat “blade” style pins instead of the traditional round connectors.

  • Turn Signals
  • Brake Lights
  • Tail Lights
  • Backup Light
  • Electric Brakes
  • Auxiliary Power
  • Ground

What to Do If Electrical Wires Don’t Match

In some cases your tow vehicle’s electrical connector may not match the trailer wiring connector. In that case you need an adapter. However, you can only adapt down (i.e. 7-Blade on the vehicle to 4-Flat on the trailer, but not 4-Flat on the vehicle to a 7-Blade on the trailer).

If the job is too big for you, seek out one of our Preferred Shops to help you do the job.

Advice, how-to guides, and car care information featured on AutoZone.com and AutoZone Advice & How-To’s are presented as helpful resources for general maintenance and automotive repairs from a general perspective only and should be used at your own risk. Information is accurate and true to the best of AutoZone’s knowledge, however, there may be omissions, errors or mistakes.

Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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