Before you tow any trailer, you should make sure it has functional trailer lights. Because installation works related to electricity scary many vehicle owners away, they prefer the experts at trailer shops to have the job done for them instead of trying to figure out how things work. However, in the simplest scenario on how to wire trailer lights, if you’ve bought a new vehicle, the only thing you will have to do is to find a factory-installed connector on it and get the right harness to attach it to the trailer.
Let’s see what types of connectors the trailering industry uses today. While the basic configuration is a 4-way flat connector that features one female and three male ends, you may come across connectors with up to seven pins for additional functions that require wiring, including electrically actuated brakes, power source for a winch, etc.
This is the most common scenario. It has three poles for basic functions (running lights, turn signals, and brake lights) and one pin for the ground. This connector is commonly found on most light-duty trailers. On the vehicle side, there will be a female connector, while the trailer/RV harness will have a male connector. When wiring trailer lights, make sure to route the harness away from anything that could damage the wires.
The basic trailer light wire colors are as follows:
GREEN – Right Turn Lights/Brakes
YELLOW – Left Turn Lights/Brakes
BROWN – Tail Lights/Running Lights
WHITE – Ground Wire
Trailers longer than 15 feet and heavier than 1,500 lbs must have a brake system – that means another circuit for hydraulic brakes. The fifth wire (blue) is meant for reverse lights; this connection is needed to disconnect the hydraulic trailer coupler or actuator when the vehicle is backing up, thus deactivating the brakes on a trailer.
Apart from providing basic functions, this connector has 2 more ports for electric brake control (blue) and 12V power supply (black or red).
7-way connectors allow for all functions provided by 6-way connectors (three basic lighting functions, electric brakes, and additional power supply), with the seventh wire for backup lights. Basically, it is another 12V circuit typically used for a reverse light / reverse lockout for trailer brakes.
- If your vehicle came prewired for towing, it may have a factory trailer harness connection (USCAR connector) in the rear bumper. This is the best case scenario, you’ll only need to buy the appropriate wiring harness with the right connectors on each end.
- If your late model car, truck, or SUV does not have a trailer package from the factory, you may go with a T-connector made specifically for your make and model. This vehicle-to-trailer wiring harness creates a standard trailer wiring connection by plugging into vehicle harness and tail light assembly, and then routing the 4-way harness to the rear end of a vehicle.
- If you own an older vehicle, chances are it will have neither trailer package factory installed nor T-connectors available for it. In this case, you can go with one of universal trailer wiring kits the aftermarket offers today. Reliable and relatively easy to install, these kits contain everything necessary to make the connection in an hour or so.
As a matter of fact, the aftermarket offers harnesses to join two connectors of any type. Even if your vehicle is not equipped with a connector, it may have a wiring plug located in the rear. Depending on the model, the location may vary from inside of trunk to under the rear floor panel. You may need to inspect your vehicle thoroughly or contact the manufacturer’s customer support to ask whether your vehicle is equipped with it and find out its location. If there are absolutely no provisions for trailer lights, you are electrically inclined or have a rough idea of how to wire trailer lights, you might consider splicing into your existing wiring. Fortunately, almost all wires you need (except for a brake controller wire) connect to your vehicle’s tail light assembly. In this case, you will need a set of wiring taps and a pair of pliers.