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How Do You Wire a 7-Pin ?

If you tow an RV, odds are you have a 7-pin trailer plug, so do you know how it’s wired? What do all those colors mean, and which connection does what?

What Is a 7-Pin Trailer Plug?

Close up view of trailer connected to a vehicle and  7-pin trailer plug

Towing a trailer of any type requires the tow vehicle and trailer to be able to signal to other drivers when they are stopping, turning, or backing up. Your tow vehicle does this automatically through its electrical system. However, trailers require signals to be sent to them to perform these actions.

The connection between your tow vehicle and the trailer is made through a wire harness. In the case of small trailers, 4-pin harnesses are used with one wire for the right side turn and brake light, one for the left turn and brake light, one for running lights, and a ground wire.

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With large trailers, including most RVs, electric brakes have become a necessity and a legal requirement in most locations. This is an extra signal that needs to be sent to the trailer from the tow vehicle through the wire harness. The additional action requires its own connection in the trailer plug.

All 7-pin connectors are round 2″ plugs that connect to all vehicle types with a 7-pin socket. Many SUVs and trucks come equipt with 7-pin sockets, and aftermarket plugs are also available.

What Do These Plugs Control?

A typical 7-pin trailer plug has a ground and controls the same lights as the basic 4-pin plug, plus reverse lights, auxiliary power (which charges your RV battery as you dive), and electric brakes.

Although the electric brakes are signaled using these plugs, they do not operate the trailer brakes. A brake controller is required to operate electric trailer brakes; it works in conjugation with a 7-pin harness. The electric brakes are controlled from the tow vehicle, and those inputs are sent to the trailer brakes through the 7-pin plug. Simply having your tow vehicle connected to your RV with a 7-pin plug does not mean you have trailer brakes!

The auxiliary wire in the 7-pin plug is connected to the tow vehicle’s 12-volt charging system. This charges your RV house batteries while you drive and allows you to run your fridge on 12-volt DC power while underway.

Not all manufacturers will use the same color code as below. However, the functions will be the same. So, confirming the colors when troubleshooting electrical issues or wiring a new plug is important. Remember, each pin has a function that will be the same on all RV plugs, but the colors may change.

  • White– Ground
  • Black – Battery 12-volt
  • Brown – Right turn/brake light
  • Red – Left turn/brake light
  • Green – Running lights
  • Yellow – Auxillary / Reverse lights
  • Blue – Electric trailer brakes

How to Wire a 7-Pin Trailer Plug

Trailer plugs can get pinched, become corroded, or have wires come loose, all resulting in needing to rewire the plug. Wiring a 7-pin trailer plug is an easy DIY project for RV owners replacing a damaged plug with a new one. If you are adding a 7-pin plug where one doesn’t exist, this is a much more involved job.

The tools necessary for this task are things all RVers should have on hand, screwdrivers and a set of wire strippers/cutters. As with all electrical projects, the first step is ensuring there is no power to the wires you’re working on.

Replacing the Plug Body Only

If the wiring is all in good condition, but you have a cracked or corroded plug, replacing the plug body is a quick and easy job. Replacements plug bodies are available for the male and female sides, and the process is the same for both.

The first step is to disassemble the plug so you can access the wires inside. Plugs will generally come apart in one of two ways. The end of the plug with the slots will pull out of the body of the plug, our the plug body will split down the middle. Either way, there will be a couple of screws holding the plug together.

Once apart, you will see the seven wires connected to the seven pins. The wire ends are held in place by screws, which will release the wires when loosened. Take note of which wire is where before removing; take a picture to double-check your work when finished. Make sure the wires are secured, so they don’t come loose before reassembling the plug.

Wiring a Plug With Damaged Wires

If you have damaged wires, the job becomes a little tougher because you will have to splice wires together. Complete plug kits that include a new junction box and full length of cable can simplify this job. The junction box will have a connection pin for each of the seven wires of the plug. You can remove the wires one by one from your old junction box, connecting them to the new box.

What if the Connection on My RV Is Different Than My Tow Vehicle?

If your vehicle has a trailer plug other than a 7-pin type, you can convert to the latter. As mentioned, the functions of plugs with fewer pins are functions included in the 7-pin plugs. When converting to a larger plug you just need to add in the additional functions. Most likely, this will be electric brakes, reverse lights, and 12-volt charging.

Companies have designed plug converters to make switching between plug styles an easy plug-and-play conversion. The 4 similar wires are simply plugged in while the extra three wires will be connected from the plug converter to your vehicle’s wire harness.

Finding the proper wires in your vehicle’s wire harness and successfully joining them to your plug converter can be tricky. This is a job that should be left to a mechanic or trailer shop unless you are fully confident that you can safely complete it.

If you have a 4-pin plug in your vehicle and a 7-pin plug in your RV, you can use a plug adapter to connect the two. Plug adapters are simply a 7-pin plug with only the 4-pin wires connected to it. It’s important to know that this means that you will only have the functions of a 4-pin plug.

Preventing Trailer Plug Damage

If you take care to keep your vehicle and RV plug ends covered, so they are dry and free of debris, it will greatly reduce the need for replacement. Using an electrical connection grease can also help with the corrosion of plug connections.

When towing, make sure you have the proper length cable between the tow vehicle and the trailer. Avoid having cable drag on the ground or not having enough cable to make turns will eliminate pinching wires and having to replace your RV plug.

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5 thoughts on “How Do You Wire a 7-Pin ?”

  1. I was fixing the plug on the church’s trailer the other day and noticed my truck’s socket cover (F-150) had everything labeled on the dust cover. It made for an easy repair knowing I had a diagram right there on the cover. So the next time your messing around with the plug, look closer. Happy Trails!

    Reply
  2. This is a somewhat simplistic explanation. Depending on the tow vehicle’s wiring to its plug, strange things can occur with plugging it into the trailer. The tow vehicle usually will have separate turn signal and brake lights. The trailer doesn’t, with the trailer’s turn signals sharing the brake lights. This can mean that when signalling it might activate the brake lights on the tow vehicle. Depending on how the plug is wired in the tow vehicle, the turn signals in the trailer will also send current to the trailer’s brake lights, since they are shared, and that can cause the tow vehicle’s brake lights to be activated at the same time because the trailer’s and the tow vehicle’s brake lights are interconnected. You don’t want this feedback to the tow vehicle’s brake lights to occur. To prevent that, you will need to insert 2 diodes (some trailer lighting kits include these), one for each side, either in the trailer’s wiring harness or (better) between the vehicle’s brake lights and the output to the plug so that current can flow to the plug but not back from the plug. First, have your assistant test for this situation while the trailer is plugged into the tow vehicle. If so, in addition to connectors and a secure way of mounting the diodes, you will need a multimeter, crimping tool, insulated wire and access to the rear brake lights while your assistant presses on the brake pedal to test your installation. Depending on the ease of access to the tow vehicle’s brake lights or identifying the correct wires in the trailer’s wiring harness, this could take 1-2 hours to remedy. To help determine the direction of the diodes, I place the positive end of a penlight battery against one of the diode’s connectors with the multimeter across the other connector and the battery negative. The diode will conduct only in one direction.

    Reply
    • Sounds complicated Jay , and I worked in a hitch shop 37 years . Any vehicle with a factory installed 7-way blade connector will be wired standard rv code (combined turn/brake light circuits ). The same goes for the trailer. When you get into “home owner wiring”, anything is possible , as color codes differ between RV and SAE and AC home wiring gets in the mix somehow as well.

      Reply
  3. Information is good, especially for beginners, but the shaky video totally destroyed any professionalism. I had to freeze this multiple times, because I was becoming nauseous. So glad I discovered it was written out below. Crazy how the colors are totally NOT what code is for wiring (green ground, white neutral, red hot, etc). Please redo this video. It is well worth the time and effort and will be very well received and shared many times.

    Reply
    • Nauseous? They must have made a new video is the past few days. I went back a second time to view this shaky video. I did not see any shaking. Perhaps you should stabilize whatever device you are looking at, or maybe they listened to you and made a new video in 48 hours.

      Reply

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