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Micro switches in the plug socket
Most cable sets no longer have any micro switches installed in the plug socket for trailer recognition.
Trailer recognition is carried out by the control unit by taking a resistance measurement of the trailer’s rear lights, or with test equipment.
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Does the trailer coupling have to be approved by the German Technical Inspection Association (TÜV)?
For all trailer couplings which have already been tested according to European standards (mark of conformity begins with an “e”), TÜV approval is no longer necessary. It is sufficient if the trailer coupling installation guide is carried in the vehicle. This serves as a general operating license.
For trailer couplings with a German mark of conformity (M or F), it is necessary to have TÜV approval, as well as to immediately record the installation of the trailer coupling in the vehicle documents.
The trailer couplings with an individual approval (TP marks of conformity) posses a separately provided approval certificate for each tow coupling. After installation of the trailer coupling, a TÜV approval is necessary, as well as making a record in the vehicle documents.
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What is meant by check control?
Equipment in a vehicle which monitors the lights and indicates any possible malfunctions is referred to as check control. This notification either takes place visually or acoustically and can be contained in information displays or car computers. Because, for these vehicles, the trailers must be operated independently from the vehicle lighting, so-called wiring harness kits for check control or extendable wiring harness kits with check control interfaces are necessary in order to rule out damage to the vehicle electrics. Wiring harness kits with check control interfaces must, in the presence if a check control system, be expanded with an extension kit.
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What is automatic level control?
If a vehicle is equipped with automatic level control, it consistently pumps itself back to the starting height during loading. This back pumping can commence straight after loading or after a short drive.
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What is meant by REC?
For models such as Opel Astra H and Zafira B built in or after 2004, the so-called REC (Rear Electric Centre) is located under the left side panel in the boot. This is a control unit pre-fitted for the insertion of a trailer control device.
For models from the Ford range, this denotes a preliminary set-up of the CAN cable ex works, which is located on the right at the rear under the cladding.
If this is not present for Ford models, then you also need an additional cable set.
Please contact your dealer for this.
It is always important to check whether your vehicle possesses the preliminaries mentioned above, as some cable sets are different, or additional cable sets are required.
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What is meant by trailer stabilisation?
The electronic trailer stabilisation is a sub-function of the electronic stabilisation programme (ESP) (also DSC, DSCT ...). The system identifies a vehicle instability caused by an accompanying trailer at a non-adapted driving speed. Through the targeted reduction of the engine torque and suitable deceleration of particular wheels, the trailer is steadied. The trailer stabilisation thereby significantly contributes to an increase in driving safety.
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What is meant by ESP?
ESP refers to the electronic stability programme.
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What is a Parktronic System (PDC)?
Parktronic is also referred to as EPH, PDC, APS, or simply as parking assistance. The space behind, and often also in front of, the vehicle is monitored and possible obstacles are visually or acoustically indicated as soon as the reverse gear is engaged. In the event of an acoustic signal, the frequency is increased (amount of time between sounds) the nearer the vehicle gets to the obstacle.
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When do I need an extension kit for continuous current or continuous current and earth?
You need this extension kit if you would for example like to tow a horse box trailer with interior lights or a caravan with fridge operation.
Optionally, there are extension kits for continuous power and charging cable. This is suitable for caravans with their own battery. This makes it possible to charge the battery during the journey.
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What is a flasher unit?
The flashing units, often also called “flasher relays”, controls the flashing impulse to the vehicle’s indicators and, where applicable, to those of the trailer. Errors in their function are indicated through a change in the flashing frequency on the indicator lights. As a general rule, the flasher unit is incorporated into the central electrics, but can also be combined with the hazard warning switch and other control units. For operation with trailers, the original flasher unit is, in combination with a relay wiring harness kit, replaced with a flasher unit with C2 function and an additional control is installed. There are flasher units with the various connection assignments which, in the event of the installation of a C2 flasher unit, must be partly adjusted using adaptors.
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What is a C2 indicator light?
The C2 indicator light must be installed within the driver’s field of vision, or is already integrated into the vehicle’s dashboard. It is responsible for monitoring the trailer’s direction indicators in correspondence with the statutory provisions. The function and failure of the trailer’s direction indicators is signalled by it working together with the original indicator lights.
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What is a ground switched rear fog light?
If the voltage-carrying cable which leads to the rear fog light has a voltage of 12 V after the light has been turned on, then the rear fog light is ground switched. For cars manufactured by Suzuki, Chrysler and Pontiac, a ground switched rear fog light may be present. You can check this by turning on the ignition and light and checking that the cable to the rear fog light already has a voltage of 12 V, whereas the rear fog light itself is turned off.
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What is meant by towing capacity?
The towing capacity is the load that the vehicle and the towbar are permitted to tow. The towing capacity of the vehicle is determined by the vehicle manufacturer. This is different depending on the type of the vehicle. The trailer loads permitted for your vehicle can be found in your vehicle documents, namely:
[1] old vehicle registration certificate
- trailing load with brakes under no. 28
- trailing load without brakes under no. 29
[2] new vehicle registration certificate
- trailing load with brakes under O.1
- trailing load without brakes under O.2
The maximum permitted trailer load of the towbar is noted in the installation guide.It is determined by the towbar manufacturer.
The towing capacity of the towbar can differ from the towing capacity of the vehicle. The value entered in the vehicle documents is always decisive! This weight must not be exceeded!
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What does tongue weight mean?
This is the load that is allowed to act vertically on the ball head from above. The tongue weight is generally between 40 and 200 kg, depending on vehicle type. The tongue weight of the trailer coupling and the vehicle must not be exceeded.
The acceptable tongue weight can be found in the vehicle manual. The tongue weight of the trailer coupling is noted on the type plate and in the installation guide.
The maximum tongue weight as specified by the vehicle manufacturer must not be exceeded.
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Where can I find the tongue weight of the towbar?
Indication of the tongue weight of the towbar can be found on the type plate and in the assembly instructions, given in kg. Please note that the specifications of the vehicle manufacturer must be observed. These can be different!
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What is the D-value?
The D-value of a trailer coupling is the basis for calculating the acceptable towing capacity. Once defined and tested using a suitable design, it remains fixed.
The D-value is determined as follows:
D [kN], GA (towing capacity) [kg], GF (acceptable total weight)[kg]

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Where can I find the D-value?
The D-value is given in kN and can be found in the assembly instructions on the type plate. The assembly instructions can be reviewed and downloaded on our homepage.
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What is meant by data bus (CAN)?
For a data bus (CAN) system, the wiring harness system is connected directly to the existing data bus system (CAN) in the vehicle. A defect on the trailer is displayed by the system already present in the vehicle. Through activation, other systems can be used such as PDC deactivation for trailer operation or trailer stabilisation. Installation of an indicator light is not necessary.
The data bus wiring harness kit is a digital system. Its function is similar to a computer network. The wiring harness system is connected to the “network” of the vehicle. In most cases, coding/activation is necessary.
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What is meant by activation or coding?
Activation means that this must be unlocked so that all of the functions of the wiring harness system can be used. This can generally be carried out through diagnostic tests in any specialist garage. Generally, functions such as rear fog light or PCD deactivation are only possible after activation.
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Does my vehicle have to be activated?
You can see whether your vehicle’s wiring harness kit has to be coded or activated by referring to the assembly instructions or online catalogue.