Trailer Wiring Diagram and Color Chart

Trailer wiring colors.
Trailer wiring colors for wire connections.

Whether you're installing a new trailer light circuit in your 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 probably goes, and why it may not be working well. This diagram shows the colors of a basic trailer wiring setup to the connector and what each wire is supposed to be connected to. Use it to install or repair trailer wiring. The will show what color is what, i.e. What does the brown wire go to?

It's never a good idea to dive into a wiring project blind. For that matter, no car or truck repair should be attempted without doing at least a moderate amount of research, and buying a proper repair manual that includes full wiring diagrams for your vehicle. I've seen too many people who start to take apart wiring only to realize they are in over their heads and have screwed things up far worse than they were to begin with. 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 4-prong connector (or 7-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 at a time, starting by checking your ground wire with a circuit tester.


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

When it comes to trailer wiring, you should never skimp, and never put your trailer on the road with questionable wiring or a lighting system that is already known to be failing. As drivers are slowing 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 well functioning brake lights on the trailer, these lights will catch the attention of drivers behind you regardless of their general state of mind. If that state of mind is more -less than -ful, you'll be ok because they will be focusing on the bright lights that are closest to them on the trailer. If your lights are dim or nonexistent, they will focus on the bright lights that are closest to them on your vehicle. Unfortunately, this means that they probably will not be stopping in time and will rear end your trailer, damaging it and the precious cargo you're hauling. 

Even if you're unfamiliar with doing automotive electrical wiring, the trailer is not too hard a job to tackle. The isolated nature of the system makes most of the electrical wires easy to follow and the connections easy to track down and test or clean. I wouldn't hesitate to guide a complete novice through the wiring of his or her trailer. 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 and almost never a danger to any one on the road. 

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