How to Wire and Install a 4 Pin to 7 Pin Trailer Adapter

Getting electrical power to your vital RV functions is not as difficult as it may seem. Sometimes you can plug a 4 pin connector into a 7 pin adapter and get all the power to your lights, and more as you need. Just make sure to attach the ground wire.

How to Wire and Install a 4 Pin to 7 Pin Trailer Adapter: The first thing you should do is test your current trailer and vehicle wiring. You may have a problem you were not aware of. Next, a buy a kit that has about 20 feet of wire length. Then position your wires where you need them and attach all wires to their corresponding colors.

That, in a nutshell, is how you wire in your 4 point connector. The key is to make sure you connect the white ground wire first. To learn more about a 4-pin connector and a 7 pin adaptor just continue to read our article.

It is filled with the information you need to know to make the right connection for your trailer.

What is a 7 Pin Connector

A 7 pin connector is a simple device that has 3 more functions than the 4 pin version. Not only does it handle the same tasks as the 4 pin- running lights, left turn signal and brake lights, right turn signal and brake lights, and ground, it comes with the ability to run the trailer’s 12-volt system, reverse lights and electric brake.

That is how the 7 pin connector got its name. It has 7 power connection options that make sure your trailer’s safety equipment is fully powered and ready to work. YO may not need to use a 7 pin connector if your vehicle already has a 4 pin installed underneath the bumper.

Some vehicles may come with both the 4 and 7 pin connector and you may find that the 4 pin will not work if you plug it into the 7 pin factory-installed option.

What does a 7 Pin Trailer Plug do

If you are new to towing, you may not understand why you need a 7 pin connector. You do not always have to have a 7 pin connector but in some towing instances it is the standard option and you need to know what it does to be able to use it correctly.

When you are towing, most towing laws make it mandatory for the vehicle being towed to have working lights. This is for your safety and the safety of those driving around you.

What the 7 pin connector doe sis operate the most lights on your trailer. The right and left turning signals, reverse lights, aux power, brake lights, taillights and the electric brake.

Each light has its own color-coded wire so you need to make sure you connect the right colors to the right function. Your owner’s manual; should help you with which wire goes to which wire.

What is a 4 Pole Connector

The four-pin connector is similar to the 7 pin in that it helps send the electrical power to your trailer’s safety lights. It just has fewer options and doe snot usually control the electric brake, aux power or the reverse lights.

What this connector controls is usually the right and left turning lights, the right and left brake lights and also the taillights. On this connector is a white wire and that is the ground. Make sure to attach it first before attaching the other wires to their trailer counterparts.

Now if your trailer has electric brakes but no back up or aux power then it is advisable and wise to use a 7 pin connector. There is also the possibility of having to take off the taillight cover to get to the right wire connections on older models.

Most vehicles since the 1990s usually come with factory-installed connectors to make your towing life easier.

What is the Brown Wire on a Trailer

For the majority of connectors out there, from 4 to 7, the brown wire handles the taillight function. It doesn’t matter the design of the connector, the brown wire is the taillight wire.

Now as it is with all thing in life, there are exceptions to the rule. In this case, it is the 7 way RV blade style connector that is the exception. If you have to use this connector to hook up your trailer, then the brown wire does not handle the taillights. That is the green wire’s job.

The brown wire on this connector operates the right turn signal and brake light. Make sure you don’t get confused and double-check which connector you are using before attaching the wires.

What is the Blue Wire on a Trailer Plug

Now this colored wire is very consistent. On all 5 to 7 pin connectors, the blue wire handles the electric break. There is an obvious exception to this rule.

The 4 pin connector never operates the electric brake. Its main duties are to operate the taillights, the brake lights, and the turning signals. Those are the most important functions when towing a trailer.

The other exception to this feature is the 5 pin flat. The blue wire in this case operates the reverse lights and no pin connection operates the electric brake when using this style of connector.

The only other wire that does not have exceptions to the rule is the white wire. That is the standard ground wire in all pin connectors no matter how many pins they have.

How do you Hook Up a 7 Pin Trailer to 4 Pin

There are 3 easy steps to connect the 7 pin trailer to a 4-pin connector.

  • First, ground your 4-pin connector. This always needs to be done first. If you do not have a proper ground, then the connector may not work for it won’t have a completed circuit.
  • Second, connect the 4 pin colored wires to their corresponding colors in the 7 pin trailer connector.
  • Third, you can either attach the 3 remaining wires directly to your car’s wiring or you can ignore them. If you choose the latter, make sure you put wire nuts or crimps on them to protect the ends of the wire.

If the electrical signal is making it through the adaptor but not to your trailer’s electrical system, then you should have a problem with a short in the trailer’s wiring. There shouldn’t be a problem at the adapter, although this is not always the case.

To make sure it is not the adapter’s fault, plug the current trailer 7 pin connector into another 7 pin connector to double-check. Or use a voltmeter. Either way, you will have fun tracking down the problem.

4 Pin to 7 Pin Trailer Adapter

This is not a hard connection to make. It works well if you have the electrical power making its way through the system through the connector and through the trailer’s electrical system.

Once you have the corresponding wires connected, you will have limited safety functions at your disposal. What you will not have is power to the trailer’s electric brakes, if it has them, the aux power if your trailer is equipped with that function or the reverse lights.

Also, you will not have the option to run the 12-volt system that can be done through the 7 pin connector.

4 Pin to 7 Pin Trailer Adapter Wiring Diagram

Wiring your 4 pin to a 7 pin connector is not that difficult. All it takes is a little know-how and a little skill putting the wires together. Anyone, including you, can do it in a short period of time.


Your owners manual should have another diagram to help you. The main concern is to make sure you connect the right colored wires together.

Now if you have different colored wires in the connector and the trailer’s wiring system, and it happens, make sure to track which color of wire goes to which function and connect the corresponding different colored wires.

Again, you should follow your manual if you run into this situation. Or you can go to a qualified tech and have them do it for you.

Some Final Words

Connecting a 4 pin connector to a 7 pin adaptor or trailer system, or vice versa, is not that difficult. All it takes is a little patience, a little know-how, and some expert advice if you are not sure.

Just keep in mind that when you are doing that, you may not be able to use all the features on your trailer. Follow the diagram above to help get some guidance on this issue.

Making sure your trailer’s lights are working will spare you the hassle the police may bring and the cost of a ticket.

Leave a Comment: