Trailer Wiring Diagram and Color Chart

How to install new wiring or repair a bad connection

Trailer wiring colors for wire connections.

Whether you're installing a new trailer light circuit in your car or truck or trying to troubleshoot trailer wiring that is not working, you'll need to understand what each wire in the trailer wiring harness does, where it likely goes, and why it may not be working well. This diagram shows the colors of a basic trailer wiring setup as well as what each wire is supposed to be connected to.

A Simple Closed System

While it's never a good idea to dive into a wiring project blind, trailer wiring is actually very simple to work on and troubleshoot. For the most part, the wiring harness that operates your trailer lights is a closed system. The only point of contact to the outside world (meaning the world that exists outside of the trailer itself) comes on the truck side of the four-prong connector (or seven-prong connector if you are using a higher end system for trailers with electric braking systems). Even on the truck side, where the trailer wiring intersects with your vehicle's wiring harness, there are only four wires to deal with. When you're troubleshooting the trailer wires, be sure you do it one wire at a time, starting by checking your ground wire with a circuit tester

Trailer Wiring Colors

The worst that usually happens with screwy trailer wiring is a blown fuse on the tow vehicle—or something wacky, like reversed turn signals or blinking brake lights. While none of these are things we look forward to when pulling a trailer, they are also easy to correct. These four colored wires make up your trailer's wiring system. Each connects to a different function:

  • Brown wire to the tail or parking lights
  • Green wire to right turn signal/brake light
  • Yellow wire to the left turn signal/brake light
  • White wire to common or chassis ground

When making your repairs or hooking up your trailer, you simply make sure these wires are running to the appropriate component as shown above.

Lights On, Always

Never put your trailer on the road with questionable wiring or a lighting system that is already known to be failing. As drivers slow down behind a vehicle that is pulling a trailer, they will often instinctively focus on the bright brake lights as a reference point for where to stop and how quickly the vehicle in front is stopping. If you've got bright, well functioning brake lights on the trailer, these lights will catch the attention of the drivers behind you, regardless of how much they are paying attention. If your trailer's lights are dim or nonexistent, those drivers will focus on the lights on your vehicle, which likely will not give them enough time to stop, which could result in an accident. While they might be deemed at fault, no one needs the headache of dealing with insurance companies—nor do you want whatever cargo you are carrying to be damaged or anyone to be injured.

Remember, pulling a trailer is never something to take lightly. Always be extra aware of everything going on around you, and give everyone the right of way.