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.
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.
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.
Trailer Wiring Color Code
How to Wire a Trailer Plug - Download complete table
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.