Trailer Wiring Diagram and Installation Help – Towing 101

Trailer Wiring Diagram and Installation Help - Towing 101

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Any vehicle towing a trailer requires trailer connector wiring to safely connect the taillights, turn signals, brake lights and other necessary electrical systems.

If your vehicle is not equipped with a working trailer wiring harness, there are a number of different solutions to provide the perfect fit for your specific vehicle. Complete with acolor coded trailer wiring diagram of each plug type, this guide walks through each available solution, including custom wiring, splice-in wiring and replacement wiring.

If you're looking to replace the wiring on your trailer, check out ourtrailer rewiring guide.

A. Custom wiring

Vehicle-specific plug-and-play harness that requires no splicing and provides a standard trailer connector

B. Splice-in wiring

Taillight converter that splices into your existing vehicle wiring and provides a standard trailer connector

Custom wiring is the ideal solution for installing trailer light wiring on your vehicle. A custom wiring harness or 'T-connector' is a vehicle-specific harness that plugs in without any spicing required and provides a standard connector output, such as a 4-way flat.

All CURT custom wiring comes with the exact components needed for a complete installation on the vehicle, including vehicle-specific plugs and an electrical converter, if needed.

Another type of custom wiring is original-equipment (OE) wiring or USCAR wiring. Select vehicles come with a standardized USCAR socket that provides a connection point for a CURT OE wiring harness.

Like a T-connector, anoriginal equipment wiring harnessplugs into the USCAR socket without any cutting, splicing or soldering required, and it provides a standard trailer wiring output, such as a 4-way flat or 7-way RV blade.

Learn more about USCAR wiring

If custom wiring is not available for your particular make and model, a taillight converter may be required to equip your vehicle with the proper trailer light wiring connection.

A taillight converter or electrical converter splices into your vehicle and provides a standard trailer plug wiring connector, typically a 4-way flat. The converter converts the vehicle's complex wiring system to be compatible with your trailer's simple wiring system. To learn more about vehicle wiring systems, check out ourvehicle wiring systems guide.

If the trailer plug wiring on your vehicle or trailer is damaged or not working correctly, you can replace the connector with a CURT splice-in plug or socket.

Plugs (trailer side) and sockets (vehicle side) are available in all standard formats and can be spliced into your existing tow wiring. Find the trailer light wiring diagram below that corresponds to your existing configuration.

If you are rewiring your trailer completely, check out ourtrailer rewiring guide.

Following the standard method for wiring a trailer connector is vital to the safety of your vehicle while towing. Connecting the wrong color wires will result in mismatched taillight functions and confusion on the road.

Use this 4-pin wiring diagram to properly wire your 4-wire trailer plug.

GreenRight turn / brakesYellowLeft turn / brakesBrownTaillightsWhiteGround

5-pin trailer wiring is very similar to 4-pin wiring, but it adds in a blue wire for the reverse or backup lights.

Not all trailers have reverse lights, so consider your own trailer as you wire in a 5-way plug.

BlueReverse lightsGreenRight turn / brakesYellowLeft turn / brakesBrownTaillightsWhiteGround

6-pin trailer wiring introduces two new functions, a wire for connecting trailer brakes and a wire for +12-volt auxiliary power.

6-way wiring is most common on gooseneck trailers and allows for use with a brake controller.

BrownTaillightsBlueElectric brakesGreenRight turn / brakesYellowLeft turn / brakesWhiteGroundBlack+12 volt

The 7-way round trailer plug is to be distinguished from 7-way RV blade plugs. The wiring connections and placement are different.

Be sure to review your own trailer connector before wiring.

WhiteGround BrownTaillights GreenRight turn / brakes RedAuxiliary power YellowLeft turn / brakes BlackReverse lights BlueElectric brakes

The SAE configuration of a 7-way RV blade plug should not be confused with the traditional configuration. Different wire colors are used for different functions.

Review your own trailer before wiring.

BrownTaillightsYellowLeft turn / brakesWhiteGroundBlueElectric brakesGreenRight turn / brakesOrange+12 voltGreyReverse lights

7-pin trailer wiring is one of the most popular wiring configruations, particularly the traditional configuration versus the SAE J2863.

Use this 7-pin trailer wiring diagram to properly wire your 7-pin trailer plug.

GreenTaillights RedLeft turn / brakes WhiteGround BlueElectric brakes BrownRight turn / brakes Black+12 volt YellowReverse lights

Note: Not all trailers are equipped with reverse lights (yellow wire). The position of this wire may vary for your own specific setup.

Note: The ground wire color on all trailer plug types is always white. Other colors vary in function, depending on the configuration.

Download complete table

The traditional 7-way RV blade format is typically used on 5th wheel trailers, travel trailers and campers. The trailer wiring colors for this configuration are different than those on the SAE configuration.

The SAE J2863 7-way RV blade format is typically used on gooseneck trailers, utility trailers, cargo trailers and equipment trailers.

Trailers are equipped with different plug types based on their electrical components. The chart below provides examples of common trailers and the types of plugs they typically use.

Utility trailer

4-way flat

6-way round

7-way RV blade

Boat trailer without surge brakes

4-way flat

7-way RV blade (rarely used)

Boat trailer with surge brakes

5-way flat

6-way round

7-way RV blade

Pop up camper

6-way square

6-way round

Travel trailer

7-way RV blade

6-way round

7-way round

5th wheel trailer

7-way RV blade

6-way round

Gooseneck trailer

6-way round

7-way RV blade

Learn more about different trailer types here. Refer to the wiring diagrams above for functions of trailer wiring colors.

Discover more great tips and how-tos on theLippert blog-- your destination for all things RVing, towing, boating and beyond!

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Trailer Wiring Diagram and Installation Help - Towing 101