Many drivers have a trailer for transporting bulky loads. In the United States, road traffic regulations stipulate that all towed vehicles (trailers, caravans, boats, etc.) must be equipped with visible operational taillights. The trailer is connected to the vehicle’s electrical system with a plug and socket.
There is a Ford 7-pin trailer wiring diagram below for the trailer and towbar socket to synchronize the signals of both vehicles.
If you own a truck or an RV and you pull a trailer, chances are you already know what a seven-way trailer plug is. Unfortunately, trailer and truck wiring degrades over time, so your 7-pin connector may need to be replaced or rewired.
If that is the case for you, stick with us as we guide you through the process. We also offer a beneficial 7-pin trailer wiring diagram Ford.
7-pin trailer wiring diagram Ford
7-pin electrical sockets are the most common in domestic vehicles. They ensure the transmission of all signals from the vehicle to the trailer/RV. If the vehicle being towed is heavy, it is essential to use a 7-pin socket as it also includes a brake controller.
Use multi-core cables with double insulation for the electrical installation (contact terminals). When wiring your 7-pin trailer plug, you must use the correct gauge cables. For reverse lights, turn signals, brake lights, and running lights, you must use a 16-gauge cable.
For battery-positive leads, ground wires, and break controller cables, you must use a 12-gauge wire. The cable harness must be housed in a crimped sleeve to protect it from weather and damage.
If you want to discover the type of seven-pin trailer plug you have, take a look at our diagrams below. Each image shows the location and color of each cable along with its function.
It is very important to remember that when wiring a 7-pin plug or socket, the wiring must be mirrored on each component. Failure to do this will cause a short circuit and could damage the vehicle’s wiring.
7-pin Small Round Trailer Plug Wiring Diagram
7-pin Small Round Trailer Socket Wiring Diagram
7-pin Flat Trailer Plug Wiring Diagram
7-pin Large Round Trailer Plug Wiring Diagram
7-pin Large Round Trailer Socket Wiring Diagram
What is a 7-pin trailer plug?
There are three main types of trailer plugs to be found on vehicles today. They are four-pin, six-pin, or seven-pin. In most of Europe, you will commonly find a 13-pin trailer plug and socket, but today we are discussing the US 7-way system. On most RVs and trucks, you will find a 7-pin connector.
A 7-pin trailer plug differs from a standard six-pin connector in that the plug has an additional connector for the electronic brake controller. This is why the 7-pin style is typically used for heavier trailers and trucks.
While round 7-pin plugs are the most common, there are also flat versions. The flat design of these plugs works in the same way, although the wiring is slightly different.
Whatever style you choose, it’s important to ensure the wiring is correct. A correctly fitted plug will allow your trailer to respond to commands and keep you and others safe on the road.
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Are all 7-pin trailer plugs the same?
Unfortunately, they are not. As we mentioned earlier, there is a flat 7-pin connector, but also, there are two different wiring standards for the seven-pin round trailer plug.
This is because the Society of Automotive Engineers (SAE) standard wiring differs from that of the RV industry. You can see the differences below.
- Green: Right turn/brake light
- Yellow: Left turn/brake light
- Brown: Tail/running lights
- White: Ground wire
- Blue: Brake controller output
- Black: Battery hot lead
- Purple: Reverse lights
- Green: Tail/running lights
- Yellow: Reverse Lights
- Brown: Right turn/brake light
- White: Ground wire
- Blue: Brake controller output
- Black: Battery hot lead
- Red: Left turn/brake light
Can I use a wiring adapter?
If your vehicle and trailer’s wiring are not a match, you might consider getting an adapter plug. These plugs are relatively inexpensive and can correct mismatches in wiring.
However, they’re only good if your trailer’s wiring is compatible. If unsure, you can also contact a professional auto electrician to ensure everything is connected correctly.
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How to fit a 7-pin trailer plug?
On most vehicles fitting a 7-pin trailer plug or socket is a pretty straightforward task. Usually, parts manufacturers provide step-by-step instructions or links to videos you can follow.
The installation steps do not differ much for different plug and socket types or other manufacturers. If you are purchasing a 7-pin plug or socket for your vehicle, it is essential that you buy a well-known brand.
Very often, you can find similar items that have been imported and are much cheaper, but these usually do not come with English fitting instructions, and in some cases, they are unsafe for road use.
If you are considering changing or rewiring a trailer plug, socket, or both, you first need to decide which type you require. The socket you choose depends on the type already available on your vehicle and the application for which you want to use it.
It could be a bicycle rack, a trailer, a caravan, a boat trailer, or a horse trailer. Or maybe a trailer socket is needed for a combination of different applications?
If the vehicle is not already equipped with a plug for connecting the trailer, a socket purchased in the store is mounted on a special plate near the tow hook. In this case, the 7-pin layout can be found in the installation guide.
After completing the installation, connect the trailer and check the operation of the circuit. If there are no issues, use silicone to seal all connections and stop all traces of water from entering the electrical parts of the connection. To prevent oxidation of the contacts, lubricate them with petroleum jelly or graphite grease.
Can I fit a towbar, trailer plug, or socket myself?
The tow hook can be installed yourself easily. All you need are basic tools. However, many problems can be caused by the electrical wiring harness connection. Besides, for the installation of the 7-pin socket, parts of the vehicle bodywork may need to be removed. Without doing this, wiring can be difficult and very inconvenient.
In some cars, cutting and drilling into the rear bumper may also be necessary. Therefore, it is best to have the towbar fitted at a car workshop unless you are very confident. Having the wiring completed by an auto electrician, you can be sure that everything will run efficiently. In addition, the cost of the service is not high.
In the case of cars with more advanced electronics, a typical user will not be able to connect the towbar. Here, the help of specialists is crucial.
How are towbar and 7-pin sockets installed on a passenger car?
Let’s follow a typical step-by-step assembly method in a popular compact passenger car model. Please note that the steps required for your vehicle may be slightly different.
- Find and purchase a towbar kit, preferably one designed for your given car model, and purchase a wiring harness.
- Thoroughly read the assembly instructions of the hook provided by its manufacturer.
- Empty the trunk, including removing the spare/temporary spare wheel if fitted under the vehicle.
- Remove the side covers in the luggage compartment to gain access to the vehicle’s electrical system. Sometimes side panels are mounted with plastic clips. It may be necessary to purchase new clips, as they may be damaged after removal.
- Remove the rear bumper. This is usually completed by unscrewing the bolts in the wheel arches, under the car, and inside the trunk. The bumper can then be removed from the rails (bumper disassembly may differ in other car models).
- Remove additional bumper covers. Detach the underbody protection covers under the bumper, if present (it is usually attached with plastic clips, which may be damaged after dismantling).
- Lift the rear of the car and place it on axle stands.
- In most cases, dismantling parts of the exhaust system is necessary. Usually, this means removing the muffler (sometimes, it will be necessary to buy new rubber hangers).
- Mechanical removal of corrosion deposits on the chassis at the bumper mounting points, if present.
- Mount the brackets and bumper bar to the car chassis using the bolts and nuts provided by the hook manufacturer. Special bolt grease can be used to make removal more straightforward in the future. A torque wrench is advisable, and the hook manufacturer will specify the force with which the mounting bolts must be tightened.
- Cut out the lower part of the bumper (if necessary) according to the recommendations of the hook manufacturer (it should include the shape of the cutout). A reciprocating saw or an angle grinder with a grinding disc is used for this purpose.
- Re-install the bumper and fit the towing hook.
- Run the dedicated wiring harness and connect the relevant wires to the correct place in the vehicle wiring loom. Modern vehicles usually provide plugs for these connections. In older vehicles, the wires may need to be spliced or soldered.
- Remount the muffler and mount the side panels in the car’s interior along with any other parts that needed to be removed.
The process of rewiring a 7-pin trailer plug is relatively simple, but you must remember to be careful. Follow our diagrams above or the manufacturer’s instructions to help you identify the correct pins for each connection.
It is important to ensure you do not damage the plug when working with it. Always unplug the cables when you are not using them, or you can cause damage.
Because 7-pin connectors are constantly under pressure when the trailer is moving, it’s essential to take good care of them.
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