Learning how to wire a six pin trailer plug doesn't have to be a weekend-long headache if you know which wire goes where and have a few basic tools handy. Most of us have been there—standing behind the truck, staring at a mess of colored wires, wondering why the left turn signal makes the marker lights blink instead. It's frustrating, but once you break down the six-pin connector into its individual parts, the logic starts to click.
The six-pin round plug is a bit of a classic. While many modern rigs use the flat four-pin or the big seven-blade connector, the six-pin remains a staple for mid-sized trailers, horse trailers, and older campers. It gives you just enough "extra" juice for things like electric brakes or a battery lead without the bulk of a larger plug. Let's get into the nitty-gritty of getting your trailer synced up with your vehicle.
Getting your gear together
Before you start stripping wires, you'll want to grab a few things. You don't need a professional shop setup, but having the right tools makes the job much cleaner and prevents those annoying "why did it stop working?" moments three miles down the road.
First, get a good pair of wire strippers. Please, don't try to use a pocket knife or your teeth; you'll just end up fraying the copper. You'll also want a small flathead screwdriver (the kind used for electronics or glasses often works best for the tiny set screws inside the plug).
A roll of electrical tape is a must, but if you want to do it like a pro, grab some heat-shrink tubing and a heat gun. This keeps moisture out of your connections, which is the number one killer of trailer wiring. Finally, a circuit tester or a multimeter will save your sanity when you're trying to figure out which wire is actually carrying the signal.
Decoding the six-pin layout
If you look at the face of a six-pin round plug, you'll see five pins circling a center pin. Each one has a specific job. While there is a "standard" color code, I've learned the hard way that you should never trust the colors blindly. Previous owners or different manufacturers sometimes get creative.
Here is the typical breakdown for a six-pin setup:
- TM (Tail Lights): Usually the brown wire. This handles your markers and license plate lights.
- GD (Ground): Usually the white wire. This is the most important connection in the whole bunch.
- LT (Left Turn/Brake): Usually the yellow wire.
- RT (Right Turn/Brake): Usually the green wire.
- S (Electric Brakes): Usually the blue wire. This sends the signal from your brake controller to the trailer's magnets.
- A (Auxiliary/12V Charge): Usually the red or black wire. This is used to charge a small battery on the trailer or run interior lights.
Notice that the center pin is often used for either the Auxiliary power or the electric brakes, depending on how your specific trailer was built. Always check the back of the plug housing—most good ones have tiny letters stamped next to the terminals to tell you which is which.
Step-by-step: How to wire a six pin trailer plug
Now that you know what's what, let's get to the actual work. Start by sliding the back shell of the plug onto the trailer wire harness. I can't tell you how many times I've finished a perfect wiring job only to realize the cover was still sitting on the bumper.
1. Prep the wires
Strip about half an inch of insulation off each wire. Twist the copper strands tightly so they don't bird-cage out when you try to shove them into the terminals. If the wires look corroded (green or dull), snip them back until you see shiny copper. Connecting to old, oxidized wire is a recipe for a bad ground.
2. Connect the ground first
Start with the White wire (GD). In the world of trailers, the ground is king. If this connection is weak, your lights will do weird things—like dimming when you hit the brakes or flickering when you use a turn signal. Insert it into the terminal labeled GD and tighten the set screw firmly.
3. Move to the lights
Next, tackle the turn signals and tail lights. Hook the Green wire (RT) to the Right Turn terminal and the Yellow wire (LT) to the Left Turn terminal. Then, take the Brown wire (TM) and secure it to the Tail Light terminal. At this point, you've got the basics covered for road safety.
4. Handle the "extras"
If your trailer has electric brakes, the Blue wire (S) goes to its designated spot. If you're running power for a winch or a battery, that's where the Red or Black wire (A) comes in. Double-check your specific plug's diagram, as some brands swap the center pin's purpose.
5. Secure and seal
Once all the wires are tucked in and the screws are tight, slide that back shell up and secure it. I like to wrap a bit of electrical tape around the area where the wire enters the plug to add some strain relief and keep the gunk out.
Why grounding is your best friend
I mentioned it before, but it's worth repeating: most "wiring" problems aren't actually wiring problems—they're grounding problems. When you're figuring out how to wire a six pin trailer plug, the ground wire provides the return path for the electricity.
If the ground is bad, the electricity will try to find another way back to the truck, often jumping through the light bulbs in ways they weren't intended. This is why you'll see a trailer where the right blinker causes every single light on the trailer to dim rhythmically. If you see that, check your white wire. Ensure it's bolted to a clean, unpainted spot on the trailer frame.
Testing your hard work
Don't just hitch up and head onto the highway. You need to test your work. If you have a buddy, have them sit in the truck and run through the lights while you stand behind the trailer.
If you're working solo, you can use a circuit tester. Plug the trailer into the truck, turn on the hazard lights, and walk back. If both sides are blinking, you're halfway there. Check the running lights by turning on the headlights. For the brakes, you might need to wedge a stick between the seat and the brake pedal if you're really on your own.
If something isn't working, don't panic. Usually, it's just a loose screw in the plug or a wire that wasn't stripped back quite far enough. Take the housing off, give the wires a little tug to see if they're seated, and try again.
Keeping it all working
Trailer plugs live a hard life. They're dragged through the mud, sprayed with road salt, and left to sit in the rain. To keep your six-pin plug from rotting away, use a little bit of dielectric grease on the pins. It's a cheap "tune-up" that prevents corrosion and makes the plug easier to pull apart later.
Also, try to keep the plug off the ground when you aren't using the trailer. If it sits in the grass, it'll soak up moisture like a sponge. Use a dedicated plug holder or even just a bungee cord to keep it tucked up under the trailer tongue.
Wiring might seem like a dark art, but it's really just a game of matching colors and making sure things stay dry. Now that you know the basics of how to wire a six pin trailer plug, you can skip the expensive trip to the mechanic and get back to the fun part—actually using your trailer.