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Trailer Wiring Diagram and Installation Help

Chapter 7

Trailer Wiring Installation Guide with Diagrams - Towing 101 - CURTTrailer Wiring Installation Guide with Diagrams - Towing 101 - CURT

Equipping Your Vehicle with Proper Tow Wiring

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 a color 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 our trailer rewiring guide.


3 Options for Installing Trailer Wiring on Your Vehicle

Custom Wiring Harness Installation OptionCustom Wiring Harness Installation Option

A. Custom wiring

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

Taillight Converter Installation OptionTaillight Converter Installation Option

B. Splice-in wiring

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

Replacement Wiring Harness Installation OptionReplacement Wiring Harness Installation Option

C. Replacement plugs and sockets

Trailer plugs and vehicle sockets to splice in and replace damaged wiring connectors

4 Pin Trailer Wiring Harness4 Pin Trailer Wiring Harness

Option A: Custom Wiring Installation

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.

Custom Wiring Harness Installation DiagramCustom Wiring Harness Installation Diagram

Custom Wiring Harness Installation Example Video


Two Types of Custom Wiring

CURT Custom Wiring HarnessCURT Custom Wiring Harness
Custom Wiring Harnesses

A custom wiring harness has multiple plugs that are used to 'T' into the vehicle's taillight assembly, drawing power directly from the taillights or from a direct battery connection and providing a standard trailer light wiring connector. While custom wiring harnesses usually require two or more connection points, splicing and soldering are still not needed.

CURT Custom Wiring ConnectorCURT Custom Wiring Connector
Custom Wiring Connectors

While some vehicles may not be equipped with a standard trailer wiring connector, they may have a special socket specifically intended for installing wiring, provided by the vehicle manufacturer. A custom wiring connector uses a single plug to plug into this factory socket and provide a standard trailer wiring connector.

Original Equipment Wiring Harness - USCAROriginal Equipment Wiring Harness - USCAR

Original Equipment Trailer Wiring for USCAR

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, an original equipment wiring harness plugs 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

7 Pin RV Blade Trailer Wiring Harness7 Pin RV Blade Trailer Wiring Harness

Option B: Taillight Converter Splice-in 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 our vehicle wiring systems guide.

Taillight Converter Installation DiagramTaillight Converter Installation Diagram

Splice-In Wiring Installation Example Video


4-Pin 7-Pin Trailer Hitch Wiring Harness4-Pin 7-Pin Trailer Hitch Wiring Harness

Option C: Replacement Vehicle and Trailer Wiring

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 our trailer rewiring guide.

Replacement Wiring Harness Installation DiagramReplacement Wiring Harness Installation Diagram

How to Wire Trailer Lights

4-Pin Trailer Wiring Diagram

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 trailer wiring diagram to properly wire your 4-wire trailer plug.

4 Way Flat Trailer Wiring Color Code4 Way Flat Trailer Wiring Color Code

 Green Right turn / brakes
 Yellow Left turn / brakes
 Brown Taillights
º White Ground

4-Wire Trailer

4 Pin Trailer Wiring Diagram - Yellow, Brown, Green4 Pin Trailer Wiring Diagram - Yellow, Brown, Green

Note: The ground wire color for a 4-flat plug is white and should be properly grounded at the trailer tongue. Read the complete rewiring guide for more.


5-Pin Trailer Wiring Diagram

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.

5 Way Flat Trailer Wiring Color Code5 Way Flat Trailer Wiring Color Code

 Blue Reverse lights
 Green Right turn / brakes
 Yellow Left turn / brakes
 Brown Taillights
º White Ground

5-Wire Trailer

5 Pin Trailer Wiring Diagram - Blue, Yellow, Brown, Green5 Pin Trailer Wiring Diagram - Blue, Yellow, Brown, Green

6-Pin Trailer Wiring Diagram

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.

6 Way Round Trailer Wiring Color Code6 Way Round Trailer Wiring Color Code

 Brown Taillights
 Blue Electric brakes
 Green Right turn / brakes
 Yellow Left turn / brakes
º White Ground
 Black +12 volt

6-Wire Trailer

6 Pin Trailer Wiring Diagram with Brakes - Yellow, Brown, Green, Blue, Black6 Pin Trailer Wiring Diagram with Brakes - Yellow, Brown, Green, Blue, Black

Round 7-Pin Trailer Wiring Diagram

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.

7 Way Round Trailer Wiring Color Code7 Way Round Trailer Wiring Color Code

º White Ground
Brown Taillights
Green Right turn / brakes
Red Auxiliary power
Yellow Left turn / brakes
Black Reverse lights
Blue Electric brakes

7-Wire Trailer (Round Prongs)

7 Pin Trailer Wiring Diagram with Brakes - Red, Blue, Yellow, Brown, Green, Black7 Pin Trailer Wiring Diagram with Brakes - Red, Blue, Yellow, Brown, Green, Black

RV Blade 7-Pin Trailer Wiring Diagram - SAE

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.

7 Way RV Blade - SAE Trailer Wiring Color Code7 Way RV Blade - SAE Trailer Wiring Color Code

 Brown Taillights
 Yellow 
Left turn / brakes
º White 
Ground
 Blue 
Electric brakes
 Green 
Right turn / brakes
 Orange 
+12 volt
 Grey 
Reverse lights

7-Wire Trailer (RV Blade - SAE)

7 Pin Trailer Wiring Diagram RV Blade - SAE7 Pin Trailer Wiring Diagram RV Blade - SAE

RV Blade 7-Pin Trailer Wiring Diagram - Traditional

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.

7 Way RV Blade - Traditional Trailer Wiring Color Code7 Way RV Blade - Traditional Trailer Wiring Color Code

Green Taillights
Red Left turn / brakes
º White Ground
Blue Electric brakes
Brown Right turn / brakes
Black +12 volt
Yellow Reverse lights

7-Wire Trailer (RV Blade - Traditional)

7 Pin Trailer Wiring Diagram RV Blade - Traditional7 Pin Trailer Wiring Diagram RV Blade - Traditional

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


Trailer Wiring Colors & Diagrams

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

7 Way RV Blade - Traditional Trailer Wiring Color Code7 Way RV Blade - Traditional Trailer Wiring Color Code

7-Way RV Blade - Traditional Configuration

Green Taillights
Red Left turn / brakes
º White Ground
Blue Electric brakes
Brown Right turn / brakes
Black +12 volt
Yellow Reverse lights

7 Way RV Blade - SAE Trailer Wiring Color Code7 Way RV Blade - SAE Trailer Wiring Color Code

7-Way RV Blade - SAE J2863 Configuration

 Brown Taillights
 Yellow 
Left turn / brakes
º White 
Ground
 Blue 
Electric brakes
 Green 
Right turn / brakes
 Orange 
+12 volt
 Grey 
Reverse lights

Differences in 7-Pin Trailer Wiring

Traditional configuration

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.

SAE J2863 configuration

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

7 Way Round Trailer Wiring Color Code7 Way Round Trailer Wiring Color Code

7-Way Round

º White Ground
Brown Taillights
Green Right turn / brakes
Red Auxiliary power
Yellow Left turn / brakes
Black Reverse lights
Blue Electric brakes

6 Way Round Trailer Wiring Color Code6 Way Round Trailer Wiring Color Code

6-Way Round

 Brown Taillights
 Blue Electric brakes
 Green Right turn / brakes
 Yellow Left turn / brakes
º White Ground
 Black +12 volt

6 Way Square Trailer Wiring Color Code6 Way Square Trailer Wiring Color Code

6-Way Square

º White Ground
 Red +12 volts
 Blue Electric brakes
 Yellow Left turn / brakes
 Brown Taillights
 Green Right turn / brakes

5 Way Flat Trailer Wiring Color Code5 Way Flat Trailer Wiring Color Code

5-Way Flat

 Blue Reverse lights
 Green Right turn / brakes
 Yellow Left turn / brakes
 Brown Taillights
º White Ground

4 Way Round Trailer Wiring Color Code4 Way Round Trailer Wiring Color Code

4-Way Round

 Green Right turn / brakes
º White Ground
 Yellow Left turn / brakes
 Brown Taillights

4 Way Flat Trailer Wiring Color Code4 Way Flat Trailer Wiring Color Code

4-Way Flat

 Green Right turn / brakes
 Yellow Left turn / brakes
 Brown Taillights
º White Ground


Common Connectors by Trailer Type

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.

 

Trailer
Type
Common
Connector Type
Alternative
Connector Types
 

Utility Trailer

Utility trailer

4-Way Flat Trailer Plug

4-way flat

6-Way Round Trailer Plug

6-way round

7-Way RV Blade Traditional Trailer Plug

7-way RV blade

 

Small Boat Trailer

Boat trailer without surge brakes

4 Way Flat Trailer Plug

4-way flat

7-Way RV Blade Traditional Trailer Plug

7-way RV blade (rarely used)

 

Large Boat Trailer

Boat trailer with surge brakes

5-Way Flat Trailer Plug

5-way flat

6-Way Round Trailer Plug

6-way round

7-Way RV Blade Traditional Trailer Plug

7-way RV blade

Pop Up Camper

Pop up camper

6-Way Square Trailer Plug

6-way square

6-Way Round Trailer Plug

6-way round

 

Travel Trailer

Travel trailer

7-Way RV Blade Traditional Trailer Plug

7-way RV blade

6-Way Round Trailer Plug

6-way round

7-Way Round Trailer Plug

7-way round

5th Wheel Trailer

5th wheel trailer

7-Way RV Blade Traditional Trailer Plug

7-way RV blade

6-Way Round Trailer Plug

6-way round

 

Gooseneck Trailer

Gooseneck trailer

6-Way Round Trailer Plug

6-way round

7-Way RV Blade Traditional Trailer Plug

7-way RV blade

 

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

   

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