How to connect a socket to a towbar by yourself

Independent connection of the socket to the towbar of the car

Sooner or later, every owner of a passenger car is faced with a situation where you can not do without the use of a towing device. Whether you are planning a trip to the sea with a rented camper, whether you want to relax on the nearest body of water with a small boat or jet-ski, or there is a need to transport bulky cargo by trailer – in all these cases, your car must be equipped with a towbar.

Many cars are manufactured with pre-installed towbars, but even if you don’t have one, it’s not difficult to weld it on. Much harder to equip it with a socket, as required by the rules for using towing devices. Here already certain knowledge in the field of electrical engineering is required.

More precisely – specific knowledge with which we intend to share with all those interested in independent connection of the towbar to the onboard power system.

Types of connectors used, pinout diagrams

The most common are several varieties of connectors used to connect the towbar socket:

• European standard seven-pin connectors;
• Seven-pin connectors used in North America;
• thirteen-pin connectors;
• Special configuration connectors.

European seven-pin connector is considered the most common, because it is used on most of the trucks as well as cars. A characteristic feature of this connector is the presence on both halves of the sockets of different types, coexisting together (“dad” and “mom”).

It is believed that this configuration is the safest when connecting the round connector to the main vehicle and the trailer in the dark. Thanks to the grooves, it is impossible to connect these sockets incorrectly, which eliminates the possibility of shorting the electric circuit and generally reduces the human factor to zero. All seven connectors are responsible for a certain function. The standard wire cross section is 1.5mm² and only the grounding wire has a higher cross section of 2.5mm².

Pin 2 is sometimes left unused. Its purpose is to provide continuous 12V power for the trailer device, which is not required in all cases.

Some craftsmen allow the possibility of schematic combination of signals for separate operation of left/right clearance lamps on the trailer. However, combining the two wires into one leads to improper operation of the lights in certain cases. In particular, the functioning of the “parking light” mode used when the trailer is parked on the curb (in this case, when the driver turns on the trailer, the parking lights on the appropriate side only come on) is impaired.

Semipin American connector is used in the USA and Canada. Its peculiarity can be called the presence of a separate contact for reverse movement of the coupling, as well as the deliberate absence of separation of signals of parking lights – they light up only synchronously.

Some models of American cars also practice the joint use of a single wire for both brake lights and parking lights. You can find commercially available connectors with different colored wires, which greatly simplifies the process of connecting/disconnecting wires.

Thirteen-pin connectors are the domain of trailer units for passenger cars. Their originality lies in the presence of several separate contacts used for the positive and negative bus. There are also reserved contacts to which you can connect additional equipment (for example, a rearview camera). This connector is designed for high amperage ratings, which allows it to be used to connect the camper with its domestic power grid, as well as to recharge an additional battery.

With proper wiring, large watercraft equipment can be connected to the connector on the vehicle side – OEM adapters are designed for this purpose.

Since the latest generations of premium trailers are equipped with their own electronic systems (like ESP, ABS) and even on-board computers, for their proper pairing with the mother electronic system also use connectors of a special kind.

Ways to connect a towbar socket

The most widespread are two methods: a simplified standard and universal.

Features of connecting the socket using the standard method:

• It is most suitable for older cars, the design of which does not have ECU, which controls the work of the power unit component. Thus, the contacts of the socket are connected to the onboard power supply through the use of factory wiring.
• The standard method is good because it is not necessary to use different splitters for wiring.
• When connecting the trailer, make sure that all of its optics work correctly in all possible modes.
• If there is an anti-theft system on the driving vehicle, it must also be connected to the trailer.
• Synchrony of operation of trailer optics with lights of the rear part of the vehicle must be ensured, for this purpose appropriate connectors are used.

After connection, if one wire is unused, it can be used to connect the second, additional swivel headlight to the trailer unit. This task can be solved in two ways: either by means of a volume clip, or by using stripping the cable insulation and subsequent soldering of the connection to the wire following from the socket outlet.

The universal method is suitable for connecting the electrical circuit of the trailer device to the onboard network of almost any car, including modern cars equipped with an onboard computer. In this case, due to the complexity of on-board electrical equipment, this task requires the use of a matching module, which is essential both when making the connection and as a means of diagnosing the functioning of the rear optics.

If you own a car that has a factory connector, the towbar socket connection diagram is usually available in the owner’s manual. Domestic models of cars are not equipped with towbars, as well as some foreign cars, so you have to connect the socket yourself using the universal (also called direct) method.

If the car has no ECU, the work on connecting the socket consists of connecting the wiring harness to one of the pads of the taillight unit. The method of connection is important. Soldering is considered the most reliable, but affordable and at the same time more labor-intensive alternative – clips – is often used.

This method is not suitable for vehicles with on-board computer control, i.e. for all modern vehicles. If you connect trailer electric devices directly, then every switching on of lights, turn signals or pressing the brake pedal will be accompanied by ECU error when electric load grows. That is why it is necessary to use a matching unit – in this case the electric power to the lights of the trailer will be supplied from the used electronic device and not from the regular terminals of the rear lamp unit. This scheme allows you to synchronize the use of the rear optics, but the trailer computer will not see.

Now let’s look at the connection options using the three varieties of connectors.

Seven pin socket pinout

This variety of connectors is most commonly used in Europe and for domestically produced vehicles. Seven pins is enough to send all the signals you need to the trailed vehicle. For the connectors pinouts are used stranded wires, covered with double insulating jacket with wire cross-section from 1.5 mm 2. The harness itself is enclosed in a corrugated tube, which protects it from mechanical damage.

Many foreign cars have a standard connector, designed for connection to the trailer. In its absence, use a store socket, which is mounted on a special platform near the towbar. The pinout of the towbar socket in such cases is performed using a universal method, which involves connecting the wires to the pins of the rear lamp block by soldering.

Usually the control signals coming from the turn signals are led to the socket by separate wires and, accordingly, are also transmitted to the trailer unit separately. As for the rest of the lighting equipment, it is possible to take the signals from only one (right or left) rear unit of the standard lighting equipment.

Pinout of the thirteen-pin socket

Recently, most European cars are equipped with 13-pin sockets, which are able to provide connection of trailer devices with a large number of consumers. If the trailer is equipped with a seven-pin socket, the appropriate adapters are used in such cases.

Description of towbar wiring diagram through 13-pin connector:

1. Yellow pin, left turn signal;
2. Blue pin, fog light (if available on the trailer unit, otherwise left unused);
3. White pin – ground for wires #1-8. Leads out to the vehicle and trailer body with a bolt connection;
4. Green pin – right turn signal, emergency lights;
5. Brown pin – right side lights, trailer license plate lamp;
6. Red pin – brake lights. Obligatory when connecting the trailer, without it the operation of the TCP is prohibited;
7. Black pin – left side lights, can be combined with the license plate lamp;
8. Pink pin – reverse lights;
9. Orange pin – 12V power from the battery, always present;
10. Gray pin – power when the ignition is on, allows you to turn on the parking lights when using the main light;
11. Combined black and white contact – ground for wire 10;
12. Combined blue and white pin – backup;
13. Combined orange and white – ground for wire #9.

As you can see, this uses three 35-amp pins to the ground and two supply wires – permanent and when the ignition is on. This diagram can be used as standard when connecting the wires to the towbar on the main and trailed vehicles.

15-pin connector pinout

This type of connector is used to interface with towed vehicles – it’s a global standard. This type of connection differs from the others in the presence of feedback, allowing you to receive information about the state of the braking system of the vehicle and control its mechanisms. Otherwise, the wiring diagram for towbar is almost the same as the 13-pin one.

Here, the green-white pin is connected to the CAN-H bus and the white-brown to the CAN-L interface.

Direct wiring diagrams

If the main car does not have a regular block to connect the towbar, it is this type of pairing of the car and the PTS, which involves connecting the wires directly to the harness of the rear optic unit. To simplify the installation procedure, it is practiced the use of connectors equipped with special plugs that correspond to each type of light device. On the back side of the device there are wires that provide a connection to the mating half of the lighting equipment.

The procedure of connecting the socket to the towbar to the car is preceded by determining where to mount the connector. Usually the lights are connected through the technological holes provided to perform lamp replacement, for the output of the wiring harness outside, you can use the drainage hole located in the bottom of the luggage compartment.

A better and more reliable connection of wires is provided by their soldering.

Often one contact is used to connect two consumers (for example, a direction indicator and an alarm system). In this case, the wire cross-section must be increased to 2.0-2.5 mm 2 , as the load on the wire increases.

All the necessary accessories for connecting the plug to the towbar can be purchased at an auto store. The use of homemade connectors is fraught with such troubles as short circuit with the following ignition of the wiring insulation.

Step-by-step algorithm of how to connect a towbar socket to a car

We will need the following materials:

• multimeter;
• socket equipped with a protective cap;
• A set of wires (if the plug and socket will be different formats);
• switching connectors (preferably – with sockets for the installation of safety devices);
• multicore/single-core cable 1.5-2.0 mm2 with two-layer insulation;
• plastic corrugated tube for laying the harness about 3 meters long;
• automotive silicone adhesive sealant;
• clamps.

How to connect the socket to the towbar:

• Make sure that the cross-section of wires is sufficient for a particular load, but it should not be excessive either;
• carefully study the wiring diagram between the car and the trailer;
• mount the socket on the vehicle using a special connector, providing the most convenient connection of the harness from the rear light assembly;
• provide connection of both direction indicators separately to the socket, all other lights (lights, brake light, fog lights, if available on the trailer) can be connected in a single piece, on the left or on the right;
• provide power to the license plate lamp on the trailer as well;
• one of the wires is fed to the ground;
• if the trailer has reversing lights, supply them with power as well.

Wiring diagram with the matching unit

The vast majority of modern vehicles are equipped with ECU – a unit that controls the operation of all systems of the vehicle. In this case, the use of standard connectors for pairing the trailer with the driving vehicle, although it will ensure that the lights on the PTS turn on synchronously with the optics on the rear unit, but the onboard computer will constantly report an error caused by the mismatch of electrical signals. To eliminate the influence of consumers of electricity on the trailer unit, use a special matching unit, which is an adapter, forcing the ECU to forget about the existence of the trailer.

Here are two variants of using a matching unit for towbar connection.

Algorithm of towbar connection with a matching unit:

• Perform all the steps of the connection option described in the previous section;
• The matching module is installed and connected to the on-board power supply according to the attached diagram;
• The matching unit is activated, and any of the lighting devices of the rear unit is turned on. If everything is done correctly, ECU will not be able to recognize the presence of the module;
• in this case you can connect the matching box to the socket. It may happen that contacts on module and trailer connectors turn out to be incompatible, in this case you should use diagrams of both connectors in order to carry out correct pinout;
• If one of the consumers is turned on and the current rating increases, as well as if one of the lights is out of order, the matching unit will go off and warn the driver about the problem by sounding a signal.

Note that the competent pinout allows you to speed up the installation procedure of the socket without the need to thoroughly check the correctness of the connection of wires.

In conclusion, here are a few recommendations that will help you to ensure long and trouble-free operation of the electrical system on the trailer unit:

Light vehicle trailer outlet pinout – towbar wiring diagram

When drivers try to plug in a trailer on their own, they sometimes have trouble with the contacts. Equipping trailers with electrical devices is a necessity that allows for the regulation of traffic regulations. Trailers that are equipped with special LED technology, which allows you to signal the moving cars behind you to turn, stop and other manipulations, significantly reduce the risk of accidents and other conflicts on the roads.

In order for everything to work correctly when connecting the trailer, the owner of the vehicle should pay special attention to the connection of lighting devices. But if the vehicle owner has never previously connected a trailer to his or her vehicle, he or she may have difficulties. As a rule, the main difficulties when connecting the trailer are related specifically to the lighting equipment. To avoid possible difficulties, you should know a few important points about the pinout of the trailer socket and the principles of its connection to the socket on the car itself.

What is pinout: definition of the term

Before attempting to connect the trailer’s pins to the car, you should know what the trailer’s receptacle pinout is. In simple words, it is a diagram of electrical connectors. You can use it to properly connect the trailer receptacle to the electrical connector on the car.

Not all drivers are aware that each make and model of car may have different plug pinouts. In addition, some motorists change the lights of the trailer, so the pinout of the new socket may also be different in this case.

Most car trailers are secured to the car with a towbar. This is a special device that not only allows you to securely attach the trailer to the body of the car, but also allows you to distribute the load evenly to the back of the car. For correct connection of the trailer and the car it is required to pay attention to the pinout of the trailer socket.

If the elements will not be connected correctly, then the braking signals, left/right pointers or other commands displayed by the LED technology in the rear of the trailer will not work. This is fraught with possible accidents and problems for the trailer owner who has failed to properly connect the parts.

Where to find a trailer tow hitch

Connecting the trailer socket on your own is not a difficult procedure if the car owner knows the pinout of the socket and has an idea of how to operate the contacts. To ensure that the trailer is securely fixed and does not create an excessive load on the vehicle, it is recommended to use a towbar.

In most models, this element is part of the basic set of equipment. But for older vehicles (e.g., 1980 and earlier), a towbar with electrical hookup capability is unlikely to be available.

To find and use a towbar, you should use the manufacturer’s instructions. This will tell you which type of attachment is recommended when using the trailer and whether the towbar is included as part of the package.

Trailer connectors: types, connection methods

A towbar, with which you can not only securely attach the trailer, but also drive the car, not all models have. But if the car is equipped with this device, it is highly desirable to use it to transport the trailer. This way the driver can be sure for the strength of the attachment of the additional structure and for its maximum maneuverability.

A towbar consists of a metal base and “stuffing” of contacts, which are connected to the electrical appliances on the trailer with a special socket and are controlled remotely by the driver of the car.

In Russia, there are 3 common schemes by which the trailer socket is connected to the load carrier:

Rosstandard receptacle. It is a connecting device that has 7 connection pins, each responsible for a specific task.

The socket according to foreign standards. In the Russian Federation there are only 7 contacts on the socket for a towbar, but foreign manufacturers have more – 13 pieces.

Special socket, custom-made or manufacture towbar by yourself.

Despite the fact that the seven-socket on the towbar is considered “Russian”, in America such devices are also actively used. Foreign sockets with 13 pins can be considered a rarity. Mostly, they are found in the owners of “home on wheels”.

Knowing the wiring diagram of the car socket for the trailer, you can easily connect all the parts correctly to properly control the tail lights. It is not advisable to guess which pin to put in where without having any idea of the layout of the circuit. At best, this can result in the lights not working when using the trailer. In the worst case, it may cause an accident due to incomplete control of the trailer.

Trailer wiring diagram: towbar receptacle pinout

Machine models manufactured since 2000 and later are equipped with various electronic devices. Each device has its own method of connection, which should be carried out in strict accordance with the diagram of the device.

The vehicle’s trailer socket pinout, which is designed for 7 connectors, includes information on:

1. Left turn.

2. Turning on fog light.

3. Grounding.

4. Turning right.

5. Right hand signal.

6. Braking (stop light).

7. Left clearance light.

Regardless of whether the car has a special transmission device for connection to the trailer, it is possible to connect lights to the inner contacts and without a towbar. The main thing is to know the pin layout and peculiarities of the procedure. 7-pin connection diagram on cars in the Russian Federation is quite common. And therefore, connecting the trailer does not cause any particular difficulties for the owners of the car.

Disassembly of the circuit by color

In order for the pinout of the towbar socket to be successful, it is necessary to use a wire made of copper, with a double level of insulation. The width of the cross section of the cores should not be less than 1.5 sq.mm. When grounding is used, the minimum cross-sectional width of the conductors is up to 3.5 sq.mm.

In some states, to simplify the connection, they issue instructions – color diagrams, with which you can quickly connect the socket out of the car with the plug out of the trailer.

So, according to the pin layout, the pinout of the trailer receptacle for a passenger car can be designated by the following colors:

1. Green.

2. white with red.

3. black.

4. Yellow.

5. Aloe pink.

6. White and blue.

7. Black and blue.

In addition, the color of the wires to connect them to the trailer may also vary. According to the standards adopted in different countries, the following variants are most common (in the sequence of connection with the trailer contacts):

1. Yellow.

2. Blue.

3. white.

4. Salad.

5. Brown.

6. Scarlet.

7. Black.

Knowing the trailer receptacle pinout and pinout location does not guarantee that the lights will be plugged in immediately and without interference. Unfortunately, some of the sockets that are located on cars by default don’t always fit the plug-in connector on specialized trailer models.

For such cases, non-standard plugs are used, which are made to order. The cost of such plugs is 20-30% more expensive. They are usually ordered by owners of rarity or rare models who can’t get a towbar that fits the socket of their car at an ordinary car market. The pinout of trailer plug in this case can be arbitrary, differing from “domestic” and foreign variants.

But usually such devices on Russian roads are rare. The reason for that is the high cost of the accessory, and that’s why ordering individual connectors and towbars is usually required for those who use commercial vehicles (for example, cleared cars from Asian countries).

How to connect the trailer, knowing the pinout of the socket?

There are 2 ways to connect a trailer with lights. The first is called “regular”. Its peculiarity is a quick connection of the plug to the sub-socket. But this option is only suitable if the towbar is equipped with a socket. Another option of wiring connection is more universal. It provides connection of the wiring contacts and signal circuits on the car.

But if the machine is equipped with an on-board computer, problems with the operation of the lights are not excluded. Unfortunately, not all on-board computers “recognize” the trailer connected in this way. That’s why its control can be complicated by appearance of information about system failure.

Using the pinout of the trailer socket connection, it is quite simple to connect all the parts. For this purpose, the left-hand contact of the socket is connected to the corresponding block on the plug, then the connection of the contact with the fog light on the trailer equipment. Proceed similarly with all the following contacts.

Despite the fact that most car models have identical pinout of trailer models, unexpected difficulties may arise when connecting to the trailer. To avoid them, after connecting all the wires through the towbar connector, you should first test them with a tester. If the device will work successfully, you can deal with the direct activation of devices on the trailer itself.

Peculiarities of connecting electronics using the pinout of the trailer socket

Knowing the wiring diagram of the trailer socket of a passenger car, it is not difficult to establish contact with the electrical appliances that are located in the external devices. But you should keep in mind some important points:

1. Stripping the insulation. When connecting the wires to the towbar connector, you should not forget about their subsequent insulation. Incorrectly connected devices can cause a short in the mains, which will result in the inability to operate electrical appliances and may cause an accident. To ensure that the harnesses are as isolated as possible, a three-meter polypropylene hose can be used. It can also be replaced with a metal hose made of corrugated material. To secure the wiring harnesses, 30 clamps of plastic material will be helpful.

2. matching unit. Unfortunately, if you have a built-in on-board computer, the procedure for connecting the trailer with a towbar is complicated. On-board computer does not perceive external electronic devices. And for normal functioning of these devices you need to buy additional equipment – a matching unit. It, too, is not always recognized by the “onboard computer”, but still allows you to control external devices with the built-in computer technology.

3. Checking with a multimeter. Experienced drivers, who prefer to do their own car repairs, have long used a special device that allows you to measure the current strength, voltage or resistance. Before you engage in the connection of the contacts, you should check whether there are no failed elements among them. A multimeter is the fastest way to do this. If there are problems with the voltage, then some of the wires should be replaced with a new one. Before working with the multimeter, it should be tested by connecting the 2 probes together and pressing “start”. A zero value should appear on the screen – this is a guarantee that the instrument is working. Checking the connected pins with a multimeter does not guarantee that all devices will work correctly. But it does allow you to determine, in the initial stages, whether there is a short in the internal network. The multimeter test should be performed according to the recommended diagram, using a red and black probe to connect to the appliances.

It is strongly advised not to try to connect the pins without knowing the pinout of the trailer socket. If the vehicle is equipped with portable electronics control circuitry, any error in connection may cause a short circuit, which will provoke failure of individual components.

Also, you should not try to connect a 13-pin foreign socket to a 7-pin plug. Some “craftsmen” manage to connect the pins selectively, which leads to problems with electrical devices. Such actions can disable a number of elements, and for cars equipped with onboard computers, such manipulations with the pinout of the trailer transport socket are even more dangerous.

Protecting Elements

The internal contacts of the socket are susceptible to the negative impact of external factors. Therefore, for the effective functioning of electrical appliances you need to take care of their protection in advance. This can be done with graphite grease. It is sold in specialized stores for car enthusiasts. Graphite grease will prevent moisture from getting to the contacts, which is one of the main causes of their deterioration (due to oxidation).