Trailer Wiring Diagrams:19 Tips Towing Electrical Wiring Installation


trailer-wiring-diagram

Are you looking for trailer wiring diagrams and helpful guide how to wire trailer, lights, Brake, routing, wires and connectors? Look no more. We´ve got you covered.

If you are planning on towing a trailer of any sort of size, then you need to have trailer wiring. It is a legal requirement to ensure that the trailer lights work. 

A lot of people believe that the whole idea of trailer wiring is ‘scary’. People just hear the idea of having to do a spot of wiring in their vehicle and it terrifies them.

Luckily for you, trailer wiring doesn’t have to be that difficult. In fact, it is dead simple, even if you do not have that much in the way of experience when it comes to vehicle maintenance.

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On this page, we want to give you an overview of some of the things that you need to know when it comes to wiring up your trailer.

We even want to give a few handy hints on ensuring that the wiring is properly protected.

Why Should You Equip Your Vehicle with Proper Tow Wiring?

It is important that you invest in tow wiring for your vehicle.

Not many people realize this but, in most states, it is a legal requirement to have lighting on a trailer.

Therefore, if you do not have proper tow wiring in place, then you won’t have lights on your trailer. This means that you are not able to legally drive your trailer.

Proper tow wiring will also help to ensure that the lights on your trailer continue to work. You don’t want the lights randomly failing while you are driving your vehicle with a trailer attached, do you?

3 Options for Installing Trailer Wiring on Your Vehicle 

Custom Wiring Installation

Custom wiring does not require you to splice any wires. It plugs directly into the wiring harness. When you are purchasing custom wiring, you have to remember that the solutions are specific to the vehicle model.

custom-wiring-installation

This means that you need to choose the custom wiring designed for your vehicle. You should be able to install custom wiring yourself. In most cases, all you need are a few simple tools.

Taillight Converter Splice-in Wiring

You should only opt for this option if you are not able to find custom wiring for your vehicle. With taillight converters, you will need to splice a converter into your vehicle’s wiring.

This will often involve stripping wires and adding your own connectors. Once this is done, the converter plugs in.

Taillight Converter Splice-in Wiring-diagram

This converter is what will provide you with a plug socket for your trailer.

Basically, the converter is making sure that your wiring system is converted over to provide the right type of power for your trailer.

Replacement Vehicle and Trailer Wiring 

This option is for those that already have wiring in their vehicle. If the trailer wiring has become damaged, then you can purchase a replacement vehicle and trailer wiring that you are able to splice into your system.

It helps to prevent the need for completely ripping out the electrical system and starting again.

This is something that you will be able to install yourself, however, you do need to bear in mind that you will likely need to strip a few wires. 

How to Wire A Trailer >> Check out the video below:

How to Wire Trailer Lights?

There are a few different ways that you can wire trailer lights. In this section, we want to run you through some wiring diagrams.

Think of this as an overview of what each wire does. This should allow you to connect everything up properly.

As always, do make sure that you consult the manual for your wiring system or vehicle if you are unsure what you need to do.

FIX YOUR TRAILER LIGHTS  – How The Circuit Works >> Check out the video below:

4-Pin Trailer Wiring Diagram

4-pin trailer wiring is the simplest to understand. As the name suggests, there are four wires here. The white wire will be the ground wire.

4-Wire Trailer

In the table below you can see the 4-pin trailer wiring color:

ColorFunction
GreenRight turn / brakes
YellowLeft turn / brakes
BrownTaillights
WhiteGround

The brown wire is for the taillights. The yellow wire is for the left turn. The green wire is for the right turn signal. 

5-Pin Trailer Wiring Diagram

On the 5-pin trailer wiring diagram, there are five wires.

The blue wire is the wire to control the brake lights. As always, the white wire is going to be the ground.

5-Wire Trailer

Your Yellow and Green wires are for the turn signals, and the brown wire is for the taillights. 

ColorFunction
BlueReverse lights
GreenRight turn / brakes
YellowLeft turn / brakes
BrownTaillights
 WhiteGround

6-Pin Trailer Wiring Diagram

6-pin trailer wiring will consist of six wires. They will be in this order:

  • Brown wire is for the taillights
  • White is ground
  • Yellow is left turn
  • Purple is reverse lights
  • Green is right turn
  • Blue is brake lights
6-Wire Trailer

Round 7-Pin Wiring Diagram

The 7-pin wiring is a little bit different from the previous wiring options. With the others, the brown wire (i.e. the taillights) is always going to be at the top.

7-Wire Trailer (Round Prongs)

With 7-pin wiring, the ground will be on the top. This will be a larger pin than the others. The pin order, from the top and clockwise is:

  • White is ground
  • Black is position lights and side markers
  • Yellow is left turn
  • Red is brake lights
  • Green is right turn
  • Brown is tail lights

The seventh wire is the AUX power. This is a blue wire in the center of the plug.

RV Blade 7-Pin Trailer Wiring Diagram – Traditional 

This option is mostly for RVs, but some companies are starting to phase it out.

7-Wire Trailer (RV Blade – SAE)

The color wires are as follows. These wires are listed clockwise starting from the top right.

  • Brown is taillights
  • Yellow is left turn
  • Blue is brakes
  • White is ground
  • Green is right turn
  • Red or Black is 12V power
  • Purple (the center blade) is reverse lights

Trailer Wiring Colors and Connector Application Chart

Connector stylePinFunctionColorDescription
4-pin1GroundWhiteGround for all trailer electrical functions.
4-pin to 7-pin2Tail Lamps
Running Lights
Side Markers
BrownPower for all normally ON lamps.
Tail, Running & Side marker lights.
4-pin to 7-pin3Left Brake Light
Left Turn Signal
YellowPower for all normally ON lamps.
Tail, Running & Side marker lights.
4-pin to 7-pin4Right Brake Light
Right Turn Signal
GreenMulti-function signal for the
Right Side Rear Tail Lamp
5-pin to 7-pin5BrakeBlueElectric Brakes Control Power
or Hydraulic Brake Disengagement (5-Pin only)
6-pin to 7-pin6BatteryRed or blackVehicle Power +12V
For trailer battery charging and accessories.
7-pin7Back UpPurpleBack Up Lamps on Trailer Tail Lights
/ Hydraulic Brake Disengagement

Different Types of Wires and Their Functions

We are going to go through the various wires that you may find in an electrical circuit on a trailer here. Although, do bear in mind that things can change.

They are not likely to change, but some vehicle manufacturers have changed up the wiring colors for some baffling reason.

So, if you are ever unsure about the function of a certain wire, then it is important that you consult the manual for your trailer wiring or vehicle.

You don’t want to hook the wrong wires up to things, after all.

It doesn’t matter where you are on a 7-pin or 13-pin system, the wire colors will always do the same job. In this section, we are only going to cover the wires that you will be able to find on both plug systems.

White Wire

The white wire should always be the ground wire on a circuit. You may sometimes see this referred to as ‘ground’ or ‘mass’.

No matter what it is called, it is the ground wire and it is vital for ensuring that the electrical circuit is complete.

You really, really do not want to be running any electrical circuit without a ground. It is just dangerous. There may be multiple ground wires on a 13-pin plug.

Brown Wire

The brown wire is the wire that is going to provide power to the right tail light. it is important that you know this.

In conventional electrical circuits, the brown wire is often used as the ground wire. However, that is almost never going to be the case when it comes to the electrical circuits on a trailer.

Blue Wire

The blue wire is the wire that is going to help control and power the mist lights on the trailer.  

Red Wire

The red wire is for the brake lights. When the brakes on the vehicle are turned on, the red wire should trigger the brake lights on the trailer too.

You do not need to have a brake controller for this to work. The vehicle will still send a signal down the electrical circuits connected up to the trailer to let the trailer know when to show that brake light.

The only thing that won’t work without a brake controller will be the actual braking system. 

Green Wire

The green wire will control the right blinker of the trailer. 

Yellow Wire

The yellow wire will control the left blinker of the trailer.

Black Wire

The black wire controls the left taillight of the trailer. 

Common Connectors by Trailer Type

In the table below you can find examples of common trailers and the types of plugs (connectors) they typically use:

Trailer TypeCommon Connector TypeAlternative Connector Type
Utility trailer4-way flat6-way round
Boat trailer without surge brakes4-way flat7-way RV blade (rarely used)
Boat trailer with surge brakes5-way flat6-way round
Pop up camper6-way square6-way round
Travel trailer7-way RV blade6-way round
5th wheel trailer7-way RV blade6-way round
Gooseneck trailer6-way round7-way RV blade

How to Protect the Wires?

Since trailer wiring is pretty exposed, it is important that you learn how to protect it. If you don’t, then you will probably be replacing your trailer wiring far more often than you would like.

The first thing that you need to do is ensure that you purchase the highest quality connectors and wires that you can afford.

The number one reason why trailer wiring fails is that low-quality components have been used.

When you are hooking up the wires, then you will want to ensure that you steer clear of any sharp parts on the chassis or the trailer.

This will help to ensure that if the wires do get knocked loose, they are not cut up by any sharp edges. Some people may also want to file down some of the sharper areas.

Although, of course, if you are going to be doing that, you want to make sure that you are no damaging the vehicle at all.

Perhaps the most important thing you can do when it comes to protecting your wires is to invest in a wire sheath.

This is basically a plastic sleeve for the wires. The wires pass through. It helps to keep them all bundled together, and the sheath will help to protect them from being damaged.

Mounting Your Trailer Wiring Harness

The instructions for mounting a trailer wiring harness here are general instructions. The installation can vary from vehicle to vehicle, so make sure that you consult the manual that came with the harness.

Begin by opening the front of the vehicle and disconnecting the battery. You can then move around to the rear of the vehicle and open the trunk, etc.

You will then need to learn how to expose the wires in the back of your vehicle. This is what varies from model to model. it will normally involve removing floor panels and unscrewing certain parts of the trunk.

Once the wires have been exposed, you are looking for the taillight wiring harness connectors. You will need to disconnect them. 

You will now need to plug in the trailer wiring harness as per the instructions in the manual. You should also attach the white wire (the ground wire) to a suitable grounding point. There should be one in the wiring area.

Attach the converter box to a flat area. There will be double-sided tape included with the wiring harness to make this easy.

You now need to run the wiring for the trailer out of the rear of the vehicle. Once it has been run out, you can reinstall everything in the trunk of the vehicle.

You can attach the wiring to the outside of your vehicle however you see fit. Make sure that it is properly protected from the elements and road debris. 

Reconnect the battery and retest the trailer lights.

How to install a wire harness for towing a trailer, boat, dolly or other things needing lights >> Check out the video below:

Trailer Wiring Adapters 

The job of a trailer wiring adapter is to convert certain trailer wiring configurations to other wiring configurations.

For example, you can use a trailer wiring adapter to convert a 7-pin plug into a 5-pin plug. You do not always need to use a trailer wiring adapter.

In fact, it is rare that you will ever need to use one. The only time that trailer wiring adapters get used is when you are looking to ensure that your trailer can hook up to your vehicle.

This is ideal for those that may regularly connect their trailer or vehicle up to other things. 

Troubleshooting Your Trailer Wiring 

To be honest, there isn’t much that you will be able to fix about the trailer wiring on your own. There are pretty much only two reasons why trailer wiring can not work properly:

  • The wires are connected incorrectly
  • There is a break or short in the circuit somewhere

If your trailer wiring has previously worked, then this rules out the first one. If your wiring has never worked, then you will want to consult the manual for your trailer or the circuit you are using to ensure that the right wires are matched up.

The most common reason why trailer wiring doesn’t work is when there is a break or short in the circuit.

if something isn’t working as well as it should, then you will need to go through the wires to ensure that the wires have no kinks or fraying. If they do, then it is important that you replace the wiring.

If the issues go beyond this, then we suggest that you get in touch with a professional that is used to dealing with trailer wiring. They will be able to diagnose the problem for you.

What to Do When Converter Shorting Out?

There are only a few issues with shorting converters that you will be able to fix yourself.

The main reason for converters shorting out is a small amount of water getting into the system.

This will only cause a brief short, and once the water has dried out, everything should be ready to roll again.

Other than that, a converter shorting out likely indicates that there is a problem with the writing system somewhere. The only way that you are going to be able to deal with the short in this case is if you inspect all of the wires leading toward the converter.

You will want to ensure that there are no damaged wires. If there are, then this could be the reason for the short. You just need to replace them.

If the short continues despite there being no clear problem with the system, then you should talk to an electrical expert. We wouldn’t really suggest that you go poking about in electronics unless you know 100% what you are doing.

There may not be a whole lot of power flowing through the electrical system in a trailer, but it is certainly going to be dangerous. 

It is exceedingly rare that you will need to replace the converter for your wiring system. If you do, then most manufacturers will allow you to purchase the converter as a spare part. You just need to splice it into your system.

What To Do When Weak Ground?

If you have a weak ground, then the problem should be fairly easy to rectify. You will need to find the place where the ground wire connects up to the trailer chassis or chassis of your vehicle.

With the power to the vehicle turned off, you will want to tighten up the screw that holds the ground wire in place. In most cases, this should fix the problem.

If you still have a weak ground after this, then you will want to remove the wire from the ground pin. You can then sand the ground pin down.

This should remove any corrosion on the pin that could be leading to a weak ground.

While everything is disconnected, you may also want to check that the ground wire has no breaks in it. Chances are that it won’t because it really won’t be moving around all that much.

However, if there are any kinks, etc. on the wire, then replace it. It should be pretty easy to do. 

How to Wire Your Car or Truck to Pull a Trailer?

T-One Connector

Perhaps the quickest way to wire a car or truck is to purchase a T-One Connector.

When you are purchasing a T-One connector, you have to remember that each connector is specific to a model of a vehicle. So, you need to make sure that you choose the right one for the vehicle model that you own.

In order to install the T-One Connector, all you need to do is located the wiring harness connector inside your vehicle.

You must unplug an existing connection and plug the T-One Connector into place. All of your trailer wiring will then run through to the T-One connector.

The whole process should take a few minutes, at the most.

Custom Hardware Kit

Custom hardware kits are also simple to use. Once again, they are specific to the various models of vehicle out there, so make sure that you choose a custom hardware kit that is suitable for the vehicle that you own.

There are two types of custom wiring options available.

The first option is a connector that will plug directly into a socket at the rear of the vehicle.

This will help to convert an electrical socket that is not typically used for trailer lights into a wiring solution that you can use to provide power for your trailer.

The second option is a custom wiring harness. You will use this if you do not have a socket on the rear of the vehicle.

The harness will plug into the taillight wiring of your vehicle. How you do this will be dependent on the vehicle that you own, so make sure that you consult the instruction manual that came with your wiring kit.

Wire Color By Vehicle Manufacturer

In the table below you can find the wire color by vehicle manufacturer:

Vehicle ManufacturerRight turn & Brake lightsLeft turn & Brake lightsTaillightsGroundBrake lightsBackup lights
GMCGreenYellowBrownBlackPink or lt BlueLt Green
FordOrange w/ Blue stripeGreen w/ Orange stripeBrownBlack or GreyRed w/ Green stripeBlack w/ Pink stripe
ChryslerBrownGreen Black or Black w/ Yellow StripeBlackWhiteViolet
JeepBrownGreen w/ Black stripeBlueBlackBlue w/ Black stripeBrown
ToyotaGreen w/ Yellow StripeGreen w/ Black stripeRed w/ Green stripeBlack or WhiteGreen w/ Red or White stripe
HondaGreen w/ Yellow stripeGreen w/ Blue stripeRed w/ Black stripeBlackGreen w/ White stripe
MazdaGreen w/ Yellow stripeBlack stripeGreen or Black stripeBlackGreen, or Green w/ Red stripe

Towing Electrical Wiring FAQs

Let’s close out this page about trailer wiring diagrams and installation with answers to some of your most frequently-asked questions about them!

What are the 4 wires on a trailer plug?

What are the 4 wires on a trailer plug? The 4 wires on a trailer are green, yellow, brown and white. The green wire is going to control the right turn and brake light. The yellow wire is for the right turn and brake light. The brown wire is for tail and running lights. The white wire is the ground.

Do bear in mind that, nowadays, there will often be more than five wires on a trailer plug. The most common option nowadays is 7-wires which adds controls for mist lights and brake lights.

What is the red wire on a trailer plug? 

The red wire is for controlling the brake lights on the vehicle. Remember, the brake lights will activate whenever the vehicle brakes.

However, the red wire does not control the brakes of the trailer. If you want to control the trailer brakes, then you will need a brake controller.

Which color wires go together?

Which color wires go together? If you are connecting up wires to one another, then the red wire should connect to the red wire, the black wire to the black wire, etc. it is pretty simple stuff.

However, if you are unsure as to how the wires should connect, make sure that you consult the manual for your wiring system. In rare cases, the colors may not match up exactly. 

What color wires go to XYZ? 

If you want to know which colors go where then you need to consult the manual for your wiring system. This will tell you the job of each color of wire. Things do tend to be standardized nowadays, so once you have a solid understanding of trailer electronics, it should be easy to wire the system.

However, we always encourage people to double-check if they are uncertain. You really do not want to be connecting up the wires incorrectly.

Are all 7 pin trailer connectors wired the same?

Are all 7 pin trailer connectors wired the same? Yes, most 7-pin trailer connectors should be wired the same. The wire colors should be standardized nowadays. Although, if you are working with a new electrical system, then it is still wise to consult the instruction manual for the system.

This way you can be sure that there isn’t anything different with the wiring. For example, imported products may have slightly different colors.

The UK, for instance, tends to use brown for the ground wire, whereas in the US it is going to be the white wire.

Why does my trailer have 5 wires?

Why does my trailer have 5 wires? If your trailer has 5 wires, it means that you have a wishbone harness on the circuit. This essentially acts as a splitter so only one wire is used to power both sides of the lights on the trailer.

If the socket has 5 connectors rather than just 5 wires, then the plug has been designed for boats that have an extra hole on the sockets. 

Do LED trailer lights need to be grounded? 

LED trailer lights do not need to be grounded. However, as with most electrical circuits, it is probably worth ensuring that there is a ground in place.

While there isn’t necessarily going to be a huge amount of power flowing through the LED trailer lights, it is still dangerous for there not to be a ground.

This helps to protect you, the electrical system, and the vehicle in the event of a power surge. 

Read also: Trailer Lights: 33 Facts You Need To Consider (Explained)

Will trailer lights work without a ground? 

Will trailer lights work without a ground? Yes. Trailer lights will probably work without a ground. However, it isn’t really suggested that you try and get them running without a ground.

It is dangerous to not have a ground on your electrical equipment, even if there is very little power flowing through it. 

How many amps does a 7 pin trailer plug? 

How many amps does a 7 pin trailer plug? The vast majority of 7 pin trailer should be 20-amps or 30-amps, though. It is rare that they are going to be any different. You don’t really want anything under 20-amps because there wouldn’t be enough power to keep the trailer lights running.

You don’t need anything higher than 30-amps because this is more than the amount of power that the trailer lights need.

How many amps do trailer lights draw?

Perhaps the simplest way to determine how many amps trailer lights draw is to look at the manual for the trailer lights, or for a sticker on the lights. Somewhere, it will list AH.

This is the number of amps that the trailer lights consume per hour. So, for example, if the trailer lights said 2AH. It would mean that the lights are consuming 2AH for each hour that they are turned on.

Trailer lights never really consume that much in the way of power and your vehicle battery should have enough juice to keep them running. 

How many amps do brake lights draw?

This depends on the brake lights that you own. Thankfully, it isn’t that difficult to work out what the power draw is.

Somewhere on the lights, or at least in the manual for the lights, it will lit list the AH. This is the number of amps that the brake lights consume per hour.

This is about as accurate as you can get. After all, you will sometimes be using the brakes more than other times. Rest assured, brake lights are never going to be a huge power draw.

What’s the difference between 7 pin and 13 pin? 

What’s the difference between 7 pin and 13 pin?  A 7-pin plug will provide only the most essential lighting for a trailer. A 13-pin plug will extend the functionality of the lighting system. For example, a 13-pin connector will allow for reverse light and mist lights.

The 7-pin plug will not be able to do either. Therefore, it is suggested that people have 13-pin plugs for their trailer whenever possible.

What is a wishbone wiring harness? 

What is a wishbone wiring harness? The purpose of a wishbone wiring harness is to split the electrical circuit that runs the lighting system in the vehicle. By splitting it, it will stop people from having to run a jumper cable between the two taillights on the vehicle.

Basically, the wishbone wiring harness is all about keeping wiring simple and ensuring that the taillights receive all the power that they need.

Can reverse polarity damage electronics? 

Can reverse polarity damage electronics? Yes, reverse polarity can damage electronics and batteries. In fact, reverse polarity can damage most of the components in an electrical circuit. Although, in some cases, this damage may not really be apparent unless the reverse polarity is something that has been happening for a while.

It is more a progressive type of damage. 

Conclusion

Remember, there is only so much that we are able to cover when it comes to trailer wiring on your vehicle.

It is important that you consult any manual that came with your system to know exactly how things connect up. However, we promise you, trailer wiring isn’t all that difficult.

In the vast majority of cases, you just connect up a couple of labeled wires and you are ready to roll. You can probably do most trailer wiring yourself, even if you do not know that much about electronics. 

References

https://www.irewiredmytrailer.com/how-i-protected-my-trailer-wiring.php

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

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

Mike Gilmour

Hi, I'm Mike, co-founder, and editor of RV and Playa. My passion is traveling (with my RV) and enjoying the day at the beach (Playa)! Well, I originally created this blog as a way to share what I've learned by experimenting with the RV lifestyle, and I want to help others develop in life through new skills and opportunities.

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