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How to Install Trailer Wiring - Chapter 7

Trailer Wiring Installation Guide with Diagrams - Towing 101 - CURT

How to Install Trailer Wiring on Your Vehicle

with Color-Coded Diagrams!

Any vehicle towing a trailer requires a trailer wiring harness 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 color-coded diagrams, 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

CURT Custom Wiring Harness Installation Option
A. Custom wiring

Vehicle-specific plug-and-play harness that requires no splicing

CURT Taillight Converter Installation Option
B. Splice-in wiring

Taillight converter that splices into your existing vehicle wiring

CURT Replacement Wiring Harness Installation Option
C. Replacement wiring

Plugs and sockets to splice in and replace damaged wiring

CURT 4-Pin Trailer Wiring Harness

Option A: Custom Wiring Installation

Custom wiring is the ideal solution for installing a trailer wiring harness 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.

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

CURT Custom Wiring Harness Installation Diagram

Two Types of Custom Wiring

CURT 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. While custom wiring harnesses usually require two or more connection points, splicing and soldering are still not needed.

CURT 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.

Custom Wiring Harness Installation Example Video

CURT Original 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.

CURT 7-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 vehicle-to-trailer wiring connection.

A taillight converter or electrical converter splices into your vehicle and provides a standard trailer 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.

Find a converter for my vehicle
CURT Taillight Converter Installation Diagram

Splice-In Wiring Installation Example Video

CURT 4-Pin and 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 the following formats and can be spliced in with just a few connectors. If your trailer needs a complete wiring overhaul, you can check out our trailer rewiring guide.

Find a replacement connector
CURT Replacement Wiring Harness Installation Diagram

Trailer Wiring Color Code

How to Wire a Trailer Plug - Download complete table

7-Way RV Blade - Traditional Configuration
Vehicle Side 7-Way RV Blade - Traditional - Vehicle Side
Trailer Side 7-Way RV Blade - Traditional - Trailer Side
Green Taillights
Red Left turn / brakes
White Ground
Blue Electric brakes
Brown Right turn / brakes
Black +12 volt
Yellow Reverse lights
7-Way RV Blade - SAE J2863 Configuration
Vehicle Side 7-Way RV Blade - SAE - Vehicle Side
Trailer Side 7-Way RV Blade - SAE - Trailer Side
Brown Taillights
Yellow Left turn / brakes
White Ground
Blue Electric brakes
Green Right turn / brakes
Orange +12 volt
Grey Reverse lights

7-Way Round
Vehicle Side 7-Way Round - Vehicle Side
Trailer Side 7-Way Round - Trailer Side
White Ground
Brown Taillights
Green Right turn / brakes
Red Auxiliary power
Yellow Left turn / brakes
Black Reverse lights
Blue Electric brakes
6-Way Round
Vehicle Side 6-Way Round - Vehicle Side
Trailer Side 6-Way Round - Trailer Side
Brown Taillights
Blue Electric brakes
Green Right turn / brakes
Yellow Left turn / brakes
White Ground
Black +12 volt

6-Way Square
Vehicle Side 6-Way Square - Vehicle Side
Trailer Side 6-Way Square - Trailer Side
White Ground
Red +12 volts
Blue Electric brakes
Yellow Left turn / brakes
Brown Taillights
Green Right turn / brakes
5-Way Flat
Vehicle Side 5-Way Flat - Vehicle Side
Trailer Side 5-Way Flat - Trailer Side
Blue Reverse lights
Green Right turn / brakes
Yellow Left turn / brakes
Brown Taillights
White Ground

4-Way Round
Vehicle Side 4-Way Round - Vehicle Side
Trailer Side 4-Way Round - Trailer Side
Green Right turn / brakes
White Ground
Yellow Left turn / brakes
Brown Taillights
4-Way Flat
Vehicle Side 4-Way Flat - Vehicle Side
Trailer Side 4-Way Flat - Trailer Side
Green Right turn / brakes
Yellow Left turn / brakes
Brown Taillights
White Ground
Towing Tip!

A bad ground connection is one of the most common causes for trailer wiring problems. A bad ground can show up as an overall lighting failure, even when the voltmeter says you have a charge. It can also create intermittent failure, causing your lights to flicker randomly. When mounting a ground wire, choose an existing factory ground connection where other ground wires are connected or use a bolt to mount the wire directly to your vehicle's chassis.

Common Plug Ends 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 Plug Ends by Trailer Type Chart

Towing 101 Table of Contents