6 Pin Trailer Plug Wiring Diagram and Install Guide

Most people meet a 6 pin trailer plug the same way. You back up to a horse trailer, look at the round connector hanging off the tongue, and realize it has two more holes than the flat 4 pin you are used to. Those two extra pins are the whole point. One runs your electric brakes while the other carries 12 volt power to the trailer for a breakaway battery or interior lights. Wiring one is not hard. The colors do most of the work for you.

6 Pin Trailer Wire Color Code

• Green wire, right turn and brake light, 16 gauge
• Yellow wire, left turn and brake light, 16 gauge
• Brown wire, tail and running lights, 16 gauge
• White wire, ground, 12 gauge
• Blue wire, brake controller output, 12 gauge
•  Red or black wire, battery hot lead, 12 gauge

Note the split. Lighting circuits run 16 gauge, but the ground, the brake power and the 12 volt hot lead all carry heavier loads, so those three step up. 14 gauge covers those three on a standard bumper pull run, which is why our 6 way cable is built that way. On long runs or heavier brake loads, step up again to 12 gauge. Undersizing them is a real problem rather than a technicality, because a thin ground or brake wire drops voltage and gives you weak brakes that feel fine in the driveway.

There is some variance between manufacturers, so check your own instructions and manual before wiring. The common swap is blue and red trading places. Test before you trust the color.

Wiring a 7 pin instead? The color logic carries over but the pin count changes. We break that one down in our guide to what the colors on 7 way trailer light wiring mean.

Round, Flat or Square. Which 6 Pin Do You Have?

Not every 6 pin looks alike, and buying the wrong shape is the most common ordering mistake we see.

The 6 pin round is what most people mean. Five pins in a ring around one center pin, usually on horse, livestock and gooseneck trailers.

The center pin is the one to check. Two layouts are in circulation. On some connectors the center pin carries the 12 volt hot lead. On others it carries the brake output. Both are common and neither is wrong, which means you cannot tell by looking. Put a circuit tester on it and confirm which one you have before you wire anything or buy an adapter. Getting this backwards sends 12 volt power into your brake circuit.

The 6 pin flat and 6 pin square show up on some imported and older trailers. Same six functions, different housing, and adapters between them are hard to find. Match the housing, not just the pin count.

Whatever the shape, the function of each color stays the same.

What You Need Before You Start

Gather everything first. Nothing kills an afternoon faster than a half wired trailer and a trip to the store.

You want a 6 way 14 gauge trailer wire run long enough to reach with slack to spare, a wire stripper and crimper, ring terminals or butt connectors, dielectric grease, a heat gun if you are going the butt connector route, zip ties, and a circuit tester. That last one is not optional. It is the difference between finding a fault in two minutes and chasing it for two hours.

If the trailer has electric brakes, you also want a 12 volt trailer breakaway kit. Most states require the breakaway on braked trailers, and it wires into the same 12 volt lead you are about to run.

Step 1. Locate or Install the Junction Box

If you already have a junction box, find it. It is usually near the front of the trailer. Take the cover off and remove the nuts from each terminal.

If you are installing a new junction box, pick a location where it can be mounted securely, like inside the trailer tongue. The location should let the wires reach without interfering with any components. If you are not installing or using a junction box at all, you can zip tie the new wiring harness to the existing wires instead.

Step 2. Make the Trailer Side Connections

Always check the manufacturer specs before making connections. The steps below cover a standard industry setup.

If you have a junction box, remove the nuts on each stud and replace the existing wiring. Cut off any excess wiring from your new cable, strip the insulation with a wire stripper, then crimp ring terminals onto the new wiring. Match each terminal to its stud, ground wire to ground wire, brake wire to brake wire. Use clips to secure any excess wire.

If you do not have a junction box, use butt connectors and a heat gun to make the same connections, and use clips to secure the extra wire.

The white ground wire earns special attention. Bolt it to clean bare metal on the trailer frame, not to paint and not to rust. More trailer light faults trace back to a lazy ground than to any other single cause.

Step 3. Connect the Vehicle Side

If your vehicle already has a 6 pin connector, plug the trailer end connector into the vehicle end connector and you are ready to go.

If your vehicle has a 4 pin connector, you need an adapter, and you need to understand what it can and cannot do. An adapter passes the four lighting functions through. It does not create a brake output or a 12 volt supply out of nothing. For those you run separate wires from the vehicle battery and brake controller.

If your vehicle has no connector at all, install a 7 way connector and a brake controller. Do not be tempted by the cheaper route of fitting a 4 pin and running an adapter off it. A 4 pin has no brake circuit and no 12 volt supply, and an adapter cannot invent either one, so a braked trailer behind that setup would have no working brakes at all.

Once the vehicle side is ready, plug in, clamp on, or splice your vehicle wiring harness into the new parts. You may need a mounting bracket. Put a small amount of dielectric grease on every connection to prevent corrosion.

Step 4. Test Everything

Test every function the wires power before you tow anything. Running lights, left turn, right turn, brakes, and the 12 volt lead. If something is not working, check for loose wires or disconnected terminals first, those are the most common culprits.

4 Pin vs 6 Pin vs 7 Pin

A 4 pin carries lights and ground. That is all. Fine for a small utility or boat trailer with no brakes.

A 6 pin adds electric brakes and a 12 volt hot lead. That covers most horse, livestock and gooseneck trailers.

A 7 pin adds reverse lights on top of everything a 6 pin carries. It is the standard on larger tandem trailers and RV towing, and it is where most new builds land. We stock the 7 way plug and a 7 way junction box for those builds.

Wiring a 6 Pin Trailer to a 7 Pin Vehicle

This is common on newer trucks. The truck came with a 7 pin socket and the trailer has a 6 pin plug.

The good news is that a 6 pin is a functional subset of a 7 pin. Every wire on your trailer has a home on the vehicle side. You are matching six functions into a seven position connector and leaving the reverse light position empty.

You have two clean options.

Use a 7 blade to 6 round adapter. This is the reversible choice and the quicker one. Check which center pin layout your 6 pin uses before you buy, because adapters are built for a specific one.

Or upgrade the trailer to a 7 way. Replace the trailer plug with a 7 pin, wire your six existing colors to their matching positions, and cap the reverse pin. Tidier, and worth doing if the trailer is staying behind that truck. A trailer electric brake wiring kit covers this, and note that it ships with a 7 way plug rather than a 6 pin, so it belongs with this upgrade rather than a straight 6 pin repair.

Match by function, never by position. Pin layouts vary and a wrong guess sends brake voltage somewhere it should not go.

Troubleshooting a 6 Pin That Will Not Work

Nothing works at all. Ground first, every time. Check the white wire connection at the frame and at the vehicle.

Lights work but brakes do not. The blue wire is the suspect. Confirm the brake controller is actually outputting, then check the blue connection at the junction box.

Turn signals flash on the wrong side. Green and yellow are swapped somewhere. Green is right, yellow is left.

Everything works until it rains. Water in the connector. Clean the pins, dry them, pack with dielectric grease.

Brakes lock or grab hard. That is a controller gain setting, not a wiring fault. Back it off and test again.

Common Questions

Can I use a 6 pin plug with electric brakes?

Yes. That is exactly what the blue wire exists for. A 6 pin carries a dedicated brake controller output, which a 4 pin does not.

What is the center pin on a 6 pin round plug?

It depends on the connector. Two layouts are in circulation, one with the 12 volt hot lead on the center pin and one with the brake output there. Both are common, so test the center pin with a circuit tester and confirm which you have before wiring anything or buying an adapter.

Is a 6 way plug the same as a 6 pin plug?

Yes. The two names describe the same connector. You will see both used by manufacturers.

What gauge wire does a 6 pin trailer plug need?

16 gauge is the minimum for the lighting circuits, meaning turn signals, brake lights and running lights. Step up to 14 gauge for the ground, the brake power and the 12 volt hot lead, since those three carry heavier loads. On long runs or heavier brake loads, go up to 12 gauge.

Why does my 6 pin have a black wire instead of red?

Both are used for the 12 volt hot lead depending on manufacturer. Test it before assuming.

Wiring is the part of a trailer people put off, right up until a light goes out on a dark road. Get the ground solid, match your colors, test every circuit, and it stays fixed.

Everything you need is in our trailer wiring and lighting parts collection.