How to Wire Trailer Lights
If you plan to tow a trailer with your truck or SUV, you'll need a trailer wiring harness to connect your brake lights, turn signals, and other elements. Not all vehicles are equipped with trailer wiring, so you may need to purchase a wiring harness for your specific vehicle.
Wiring trailer lights isn't as hard as you might expect, but things can get complicated fast if you have to use custom wiring to get your vehicle connected to your trailer.
Let's take a look at some trailer wiring basics.
Trailer Wiring Options
There are many different configurations for wiring a trailer, but the most popular one is the 4-way configuration. It's called a 4-way configuration because it only needs four wires to connect the trailer tail lights, turn signals, and brake lights. The green wire represents the right brake light and right turn signal. A yellow wire connects the left brake light and left turn signal. The brown wire powers the side marker lights, and the white wire serves as the ground.
Curt 4-Way Connector Plug & Socket
Beyond the 4-way system, there are also 5-way, 6-way, and 7-way systems, but they all build on the 4-way system. For example, an additional blue wire in the 5-way configuration powers an auxiliary system like electric brakes. If your vehicle has a connector for a 6 or 7-way system, then it's easier to simply purchase an adapter so you won't have to splice in a new connector.
Curt 7-Way Trailer Wiring Harness
Connectors By Trailer
Different trailer types and trailer hitches often have common connectors, so the trailer hitch harness you need might depend on your trailer. For example, a utility trailer and a boat trailer without surge brakes usually come with a 4-way flat connector.
Alternative connectors include a 6-way round and 7-way RV blade. A boat trailer with surge brakes usually comes with a 5-way flat connector and a 6-way round or 7-way RV blade are alternatives.
A pop-up camper usually comes with a 6-way square connector, but a 6-way round connector is an alternative. Travel trailers are generally equipped with a 7-way RV blade connector, but 6-way and 7-way round connectors are alternatives. You'll usually find a 7-way RV blade on a 5th-wheel trailer and a 6-way round connector on a gooseneck trailer hitch.
7-Way RV Blade Trailer Wiring Harness
4-Way Trailer Wiring System
Start by connecting the ground to the trailer frame. Use a self-tapping screw and ring terminal to attach the white ground wire to a clean bare section of the trailer frame. Each trailer light should be grounded separately on the frame.
Run the other wires along the trailer frame to the lights. There are a few ways to do this. Feeding the wires through the hollow frame offers the best protection, but you can also drill into the frame and add grommets, or you can use zip ties to secure the wires to the frame.
After you have the wires in the right location, you can connect to the trailer lights. Each light should have three wires. One connects to the brown running light wire, a green or yellow wire that connects to the turn and brake lights, and the white ground wire.
If your vehicle already has a 4-way connector, all you have to do is plug the trailer connector into the vehicle connector. If not, then you'll have to use custom wiring to either splice into or plug into your vehicle's existing lighting.
4-Way Custom Wiring Harness
7-Way Trailer Wiring System
After the 4-way system, the 7-way is another popular way to wire a trailer. This system adds three additional pins for electric brakes, reverse lights, and a 12V connection. The additional wire colors are generally blue, red, black, or purple.
Start by locating or installing a junction box. If you need to install one, the usual place is on the inside edge of the trailer tongue.
With a junction box, you can simply add a 7-way connector by removing the nuts on each stud of the junction box. Without a junction box, you'll need to connect the 7-way to your existing wiring with butt connectors and a heat gun.
Connecting the 7-way system to your vehicle is the same as the 4-way. If you have an existing 4-way plug, you'll need an adapter to provide the extra pins for the 7-way. Otherwise, you'll need to go the custom wiring route.
if you don't have any experience in DIY electrical wiring for vehicles, you can easily get a trailer wiring kit at H&H and have it installed at any of our locations. To ensure that you get the proper trailer wire harness for your vehicle, use the vehicle selector below to browse our catalog.