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?
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.
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.
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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