How to Wire a 4 Pin Trailer Plug: Step-by-Step Guide

Trailer wiring can be one of the most daunting aspects of your towing setup, especially if you don't have the necessary experience. You don't need to have a professional install your wiring if you want to turn your car into the perfect tow vehicle; installing 4-pin wiring can take a few hours, but it is a manageable task with rewarding results.

In this article, we'll guide you through the process of installing 4-pin wiring on a trailer plug. Our guide will talk about color coding, wiring a 4-pin trailer plug from your trailer side and your car side, equipping your vehicle for proper towing, and a few bonus tips that might come in handy.

Color Coding for 4 Pin Trailer Wiring

An essential aspect of trailer wiring is color coding. Understanding the standard color code for a 4-pin wiring harness is vital before starting your project and making connections.

The type of color code that you have for your wiring harnesses generally depends on your manufacturer. No one makes them the exact same way, but some standards allow for common ground and easy identification. Typical trailer wiring colors include brown, yellow, green, brown, and at times red and black wires.

Here's a walkthrough of the general color coding system for wiring a 4-pin trailer plug:

• Green wires have the function of powering your right turn signal and right brake light feature on your brake controller. Attach the green wire to the vehicle's wiring harness on the vehicle area, indicating "turn right." You should, in turn, connect the green wire to the trailer's right turn signal in your trailer area. The suggested minimum gauge for green wire is 18.
• Yellow wires have the role of powering the left turn signal and left brake light. You should attach the yellow-colored wire to the vehicle's wiring harness on the vehicle wiring side, indicating "turn left." You connect the yellow wire to the trailer's left turn signal on your trailer wiring side. The suggested minimum gauge for yellow wire is 18.
• The brown wire is used to power the running lights and tail lights. Attach the brown wire to the vehicle's wiring harness on the vehicle area where your taillight is. Finally, connect the brown wire to the trailer's taillight on your trailer wiring side. The suggested minimum gauge for brown wire is 18.
• White cables have the function of allowing you to ground your vehicle. You should attach the white wires to the vehicle's wiring harness, where you will find an uncoated metal. You should, in turn, connect the white wire to your trailer's ground point. The suggested minimum gauge for a white wire is 16. The white wire is extremely important as it is the power wire. The white supplies power to the brake lights, reverse lights, turn signals, tail lights, turn signal, and add auxiliary power.
• If your manufacturer used red and black wires instead of a green wire, brown wire, and yellow wire, the red wire is for your brake lights and turn signal, and the black wire is generally for running lights.

Keep your vehicle's owner's manual on hand to be sure that you are making the correct connection. Alternatively, you can access your vehicle's circuit system with a circuit tester that will allow you to test your wires to determine their function.

Behind your vehicle's taillights, you'll find your vehicle's wiring system. You can find corresponding connections by activating the functions of your harnesses on your circuit board.

How to Wire a 4-Way Plug

The foundations for success have been set out. Your wires are in order, so you can start preparing to wire your 4-pin trailer plug. Let's get into the guide by starting with your trailer wiring side!

Prepping for Trailer Wiring Side Connections

Step 1: Set up Trailer Wiring

It's always a good idea to be as prepared as possible. Gather all of the tools that you'll need, including your trailer's new lights. Remove your trailer's old lights before installing your trailer wiring. If you do not need to replace your wiring, then that's fine, but you can purchase new trailer wiring should the need arise. Trailer kits can also be quite handy as they include trailer lights in their package.

Step 2: Ground Wire Connection

One of the most important things to remember when connecting your white ground wire is to ensure that the area is clean. So, be sure to clean your trailer frame prior to connecting your white ground wire to it. You should diligently remove any oil residue, flaking paint, or dirt buildup and treat corroded areas affecting the ground location.

Once everything is in order, secure your trailer frame and white ground wire by attaching the two components. The ground wire connection can have an immense impact on the rest of your wiring, so it's best to work as carefully as possible. Ensure that your trailer lights are individually grounded by the side of your trailer frame to minimize ground wiring complications and compromise your wiring system.

It's standard for the trailer connector plug to extend approximately 2 to 3 feet past the trailer tongue, so this is where you will make your ground connection. Make your ground connection behind the tongue of your trailer, should your trailer fold.

Step 4: Make the Connections

If you're ready to start connecting your wires, you can follow these guidelines to connect your wires:

• Use a crimper to remove your wire's insulation
• Connect the appropriate wires by using butt connectors and a reliable heat gun
• Connect your ground wires

Note that your lights will be connected to the main harnesses using 3 wires which will be your brown, yellow, and green wires or red and black wires, depending on your manufacturer. Your white ground wire should be firmly connected to your trailer's frame.

Vehicle Wiring Side Connections

Wiring your vehicle should be a breeze now that you have successfully prepared and wired your trailer side.

Step 1: Setting your Vehicle for Installing Wiring

Assuming that you already have a 4-pin trailer plug, this process should be quick and easy. You can now proceed by plugging in the trailer side of your connector into the vehicle side. It is essential to correctly equip your vehicle for towing but more on this later in the guide.

If you do not have a 4-pin trailer plug as of yet, then you can add one to your trailer. However, you have to understand that adding a 4-pin trailer plug is not a one size fits all situation. Consider your vehicle's production year, model, and the manufacturer to install custom wiring.

Step 2: Ground Connections on Vehicle Wiring Side

Connecting the ground wire is probably one of the most sensitive aspects of wiring a 4-pin trailer plug. However, it is a straightforward procedure! All that you have to do is connect the white ground wire to your stripped and prepped vehicle frame.

Step 3: Connecting the Vehicle Side

Congratulations! You are heading towards the final steps in successfully wiring a 4-pin trailer plug. At this step, you can securely plug, splice, or clamp your wiring harness into your vehicle's lighting. As mentioned before, this connection depends on your vehicle's model, so be sure to check your vehicle's owner manual.

At this point, you can test your connections to see if they were indeed successful. You can do this by connecting your trailer area and vehicle side. If it lights up, then everything should be in order! But, if you find that it doesn't light up, you can adjust your wiring and connections as needed.

A List of Essential Tools and Supplies for Wiring a Trailer Plug

• Crimping tool or pliers
• Cutter
• Stripper
• Metal clips
• Dielectric grease
• A 4-pin trailer wiring connections kit containing green-, yellow-, brown-, and white wires (or red and black wires)
• Heat gun
• Butt connector
• Zip ties
• Terminal wires
• Power drill with a small drill bit attachment
• Terminal connecter
• Wire tubing
• Circuit tester
• Stainless steel screw
• Washer

This list of tools will come in handy for when 4-pin trailer wiring. Manufacturers typically add all the tools and connections needed to standard trailer wiring kits; however, this is not the case with all manufacturers. These tools are essential, but some of them are interchangeable.

Another key step to take when concealing your wires is to use heat shrink tubing on your butt connectors. You can conceal the wires that are crimped in the connector by melting them with your heat gun. The plastic tubing protects your wires from abrasion and can prevent corrosion. The cutters are perfect for stripping or cutting your wires, whereas the pliers or crimping tool can be used interchangeably to wire your connections.

The zip ties allow you to keep your wires organized to avoid having loose wires dangling all over the trailer body.

How to Install a 4 Pin Trailer Plug

Refer to a trailer wiring diagram

Now that your vehicle side and trailer side are prepped for the installation of your 4-pin trailer plug, you should be able to install a 4-pin trailer wiring on your vessel as a boat trailer and utility trailer.

A crucial step is referring to a trailer wiring diagram; this allows you to visualize what is needed of you. A trailer wiring diagram also indicates the colors well and shows you the connection points. A trailer wiring diagram is also typically labeled, which adds some much-needed guidance for you on your trailer wiring experience.

A 4-pin trailer wiring diagram can be found below. This trailer wiring diagram has great visuals and labels that show you where to find the trailer connector, right side marker lights, left side marker lights, clearance lights, rear marker lights, and where to ground to the trailer frame.

Installation

• You can wrap your trailer wiring around the front of your trailer, but it can give off a chaotic look, and it doesn't protect your wiring. Instead, you should pass your trailer wiring through the area where your ball hitch and trailer frame are attached. It should have a hollow opening which adds added security for your wires. You can also run wires along the side of your trailer.
• You can feed your spliced wires to the brake lights and turn lights from the trailer frame. But if you prefer to have your wires separated, you have to ensure that your connector plug is not too short to reach your vehicle. This will allow you to run one wire at a time. You can do this by running your green wires and yellow wires through separate side markers, as seen in the trailer wiring diagram linked above.
• The white wire, as mentioned before, is a very important element as it is your power wire and provides auxiliary power. Attach your white wire to the trailer after cutting it down to 1 to 2 feet, and then remove about half an inch of its insulation. You can now proceed to use the heat gun to melt the heat shrink tube after crimping the connection. Now, use a stainless steel screw to attach your white wire to your trailer frame after drilling a pilot hole into the trailer frame.
• At this point, cut your brown wire close to the marker light wire and remove about an inch of the insulation to expose the wire strands. Twist the brown wire and your marker wire and proceed to insert the wires into your butt connector. After determining the distance between this connection and the remaining marker light, use some of your remaining brown wires to meet this length.
• Now, make another connection by using a butt connector to attach your measured brown wire to the polar marker light wire. Join your connection by twisting the ends together, and insert this second connection into the polar side of your butt connector. In order to seal your brown wire and marker light wire connection, you should crimp it and use heat shrink. You should do this for the back and front of your trailer.
• Your final milestone for the process of installing a 4-pin trailer plug is here! You now connect yellow wires to the left tail light and connect your green wires to the right tail light. Refer back to the trailer wiring diagram to ensure that your connections and trailer wiring are correct.
• Everything should work, and you should have a reliable connection! If you encounter issues, refer to our tips for wiring a 4-pin trailer plug later in the article, it might help.

How to Replace a 4 Pin Trailer Plug

A trailer plug should be protected against harsh elements. If your trailer plug has become corroded, damaged by abrasion, or is simply broken, then you need to replace it if the trailer plug cannot be repaired.

1. Wear safety equipment such as eye protection and gloves.
2. If the damage to your trailer plug is not extensive, you can buy a trailer plug extension. Start by cutting the trailer wiring connection at the vehicle area. At this point, you should add your new plug by stripping, splicing, and soldering the old wiring harness to your new plug and wiring. Prevent future wear and tear by taping your connection and heat shrinking it.
3. You can also buy a new plug to replace your damaged 4-pin trailer plug. Make sure the plug is easy to install; often, you simply cut off the plug that's broken, connect your preexisting wires to the new plug, and secure it.

How to Wire Trailer Lights

If your trailer lighting is faulty or broken, then it's best to replace the trailer lighting instead of patch-fixing issues. Before attempting to wire your trailer lighting, have a look at this trailer wiring diagram.

1. Wear safety equipment such as eye protection and gloves
2. Test your 4-pin trailer wiring connections by using a circuit tester. Once you've established that your wires have power running through them, you should move onto your frame and trailer connector to ensure connectivity. In your prepping process, ensure that the ground wire is securely connected to the trailer frame.
3. Remove all of the remaining old wiring, and replace it with the new wires by stranding the new wires in as you remove the old wires. Thoroughly clean the frame and plate by using a grinder; you need a clean surface.
4. Connect your light to your refurbished plate by connecting the black wire to your dual wires. Connect the side light wires to the central wires using metal clips. Attach the wire that requires power to the clip and use the metal tab to crimp it down.
5. Repeat the process on the other side of your frame
6. Enjoy your new trailer lighting!

Top Tips for Wiring a 4-pin Trailer Plug

• Always start your trailer wiring project by doing basic troubleshooting and testing your connections. You have to know what you're working with and what to expect! Inspect your butt connectors to ensure that everything is in order.
• If the butt connector is faulty, you can troubleshoot this issue by reconnecting your white wire, which is always the white wire. If the white wire is installed incorrectly, it will cause a power outage and affect all the lights and remaining wires.
• If you suspect that your trailer wiring has been installed incorrectly, then consider using a connection tester to test the connections. Invest in a good quality connection tester as cheaper alternatives might not work properly.
• Trailer wiring troubleshooting can be a trial and error situation. If you suspect that the wiring harness on your vehicle is faulty, you can invest in a circuit tester. A circuit tester allows you to run diagnostics on each pin on the connector plug. In turn, you will be able to determine the source of your trailer wiring issues. Alternatively, connect your trailer to a tow vehicle via its trailer plug to determine what your trailer wiring problem is.
• You have to start strong if you want long-term results, especially when it concerns the wire specs for your specific trailer. Trailer wiring industry standards for wire gauge size is 16 gauge, but thicker wires do exist and are often preferred. Trailer wiring can be very specific to your vessel: utility trailers might have different gauge size needs than boat trailers, for example.
• Your 4-pin trailer wiring kit should have wires that are long enough for your trailer. The average length for a trailer wire is 20 feet, so do not buy anything below this length as you might run into complications.

Frequently Asked Questions

What's the difference between 4-pin trailer wiring and 5-pin trailer wiring?

There are many similarities between 4-pin trailer wiring and 5-pin trailer wiring; however, in a 5-pin trailer, a blue wire is added for backup lights and reverse lights.

6-pin connections are also available - these have a wire for the battery connection and one for trailer brakes.

Which wire is important for the vehicle battery?

The ground wire or T connector connects the vehicle to the negative side and generally provides power to the system. A T connector is one of the most important wires.

What type of trailers use 4-pin trailer wiring?

4-pin trailer wiring is popular amongst light-duty trailers such as boat trailers and utility trailers.

Final Takeaway

Trailer wiring can be a long process, however, if your break it down into phases, it will be a lot easier for you. A trailer wiring diagram is a useful tool to have a visualization of what you're meant to do, so always utilize it. You should be ready to take on any trailer wiring task explained in this guide should you follow the instructions and tips.

Always wear protective items when taking on these tasks. You do not want to injure yourself while trying to fix your boat trailer or utility trailer!

Resources

https://www.etrailer.com/Wiring/Hopkins/HM48190.html

https://axleaddict.com/auto-repair/Tips-for-Installing-4-Wire-Trailer-Wiring

https://www.truckspring.com/trailer-parts/trailer-wiring/wiring-information-diagram.aspx

https://www.curtmfg.com/towing-electrical-wiring

https://www.etrailer.com/faq-wiring-4-way.aspx

https://www.caranddriver.com/car-accessories/a38333142/trailer-4-pin-connector/

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