Towbar wiring kits

Glossary towbar wiring kits

Trailer auto-detect

The Trailer Auto-Detect indicates to the towing vehicle or control unit whether or not a trailer is attached. This information is used to control the turn signals, acoustic parking system, and other control functions. A microswitch installed in the socket selects whether to transfer the information to the control unit or directly to the electronic system of the vehicle. In the current version, an attached trailer is usually electronically detected by the electrical load of the trailer lighting and the required information is passed on accordingly.

Trailer control unit

This is the designation for control units that are partially or completely supply the trailer lighting. This is controlled via the tail lights and the continuous positive to be attached to the control unit supplies the entire trailer. In vehicles without Check Control, the turn signals and rear fog lights are supplied via the control unit. In vehicles with Check Control, the entire trailer is supplied via the control unit so that the vehicle electronics are only loaded minimally. The turn signals do not have to be replaced.

Turn signals

The flash unit, often referred to as a "flash relay", regulates the flash pulses sent to the vehicle and, if attached, also to the trailer. Malfunctions are indicated by changes to the flashing rate of the control lights. In most cases, the flash unit is integrated with the main electrical system When using trailers, the original flash units are replaced in most cases by flash units with C2 capability and an additional control is installed. Flash units are available in a wide range of pin configurations, some of which require additional adapters in order to install a C2 flash unit.

C2- indicators

These are popular indicator lights that drivers use to monitor the trailer turn signals, as vehicle regulations require. These are usually green indicator lights which are controlled by the flash unit. The indicators must be situated within the driver's visible range; with some vehicles these are already installed in the dashboard or they need only be retrofitted. These indicate to the driver whether the trailer turn signals are properly functioning and work together with the original indicators.

Check-Control (CC)

Check Control (abbreviated as CC) refers to the equipment in a vehicle which monitors the the lights and indicates any malfunctions. Many vehicles are available both with and without CC. These are optical or acoustic indicators that may be integrated with info displays or dash computers. Since trailers attached to these vehicles have to be operated separately from the rest of the vehicle lighting, special CC electrical kits or expandable kits with a CC interface are required in order to eliminate causing damage to the vehicle electronics. Electrical kits with a CC interface require a CC expansion kit in order to function with a CC system.


A crimp socket generally refers to sockets where the contacts are already attached to the wire set and prefabricated in a contact holder.


In accordance with DIN/ISO 11446, contact no. 9 of the 13-pin socket is responsible for supplying continuous power directly from terminal 30 of the battery. Most of the 13-pin electrical systems come equipped with an appropriate connector (min. 2.5 mm² cross-section, max. 20 A) and corresponding earth at contact no. 13.


The installation instructions provide general information on how to install the electrical system or attach the trailer towbar for the given vehicle.

Disabling the acoustic parking system (APS)

The acoustic parking system (APS) is sometimes referred to as parking distance control (PDC), Parktronics, or EPH (in Germany). This system monitors the distance behind the vehicle and potential obstacles are optically or acoustically indicated whenever the driver switches into reverse gear. To avoid incorrect information, the acoustic parking system should be turned off when operating with a trailer. When attaching and unattaching the trailer, APS can be disabled and enabled automatically using the microswitch in the socket, or as with most Westfalia electrical kits, automatically using the control unit.

Vehicle-specific connection

All of the vehicle connections are made using the available connections so as to avoid connection errors and save time.

Charging line

In accordance with DIN/ISO 11446, contact no. 10 of the 13-pin socket is intended as the charging line for the trailer battery. Most of the 13-pin electrical systems come equipped with an appropriate connector (min. 2.5 mm² cross-section, max. 20 A). The charging line is connected to the battery by an uncoupling relay as soon as the ignition is turned on or the motor starts running.

Disabling the rear fog lights

In accordance with ECE R48, the rear fog light of the towing vehicle can be disabled when towing a trailer. When attaching racks (e.g., bicycle racks) with lighting units, they have to be turned off in order to reduce glare. This is automatically enabled/ disabled in one of the following ways:

  • Using a mechanical disconnecting contact in the socket or using a microswitch,
  • Using an additional cutoff relay,
  • Automatically by the control unit as soon as the trailer is detected.
7-pin socket in accordance with DIN/ISO 1724

Simple connection (N version), not water-tight, sufficiently fulfils the original legal requirements. It is not possible to include continuous positive or reverse lamp signals, because all of the lines are already in use. As of 01 January 1991, reverse lamps are mandatory on all vehicles and racks (e.g., bicycle racks) with reverse lamps must also include all of the other light signals, thus meaning that the 7-pin socket is no longer sufficient.

7-pin socket in accordance with DIN/ISO 3732

Simple connection (S version) as an extension to standard 7-pin socket for reverse lamps and continuous positive, pin connections not identical to standard 7-pin socket (sometimes used in GB).

7-pin socket in accordance with DIN/ISO 11446

Simple connection, water-tight with simple handling. Corresponds to automobile industry standard. Signals such as reverse lamp and continuous positive can be suitably transferred and reserve lines are available, allowing for additional options that are especially useful in camping applications.

Top-Tronic (T)

This is the designation for electrical systems that work with a trailer control unit and usually do not require modifications to the dashboard electronics. Malfunctions in the trailer turn signal system are indicated by an increased flashing rate of the turn signal indicators in the vehicle. No additional C2 lights are required.

7- und 13-pin

7-pin electrical kits are usually used for normal trailers which require neither continuous power nor a charging line. It is not possible to connect reverse lamps. The 13-pin electrical kits allow you to use reverse lamps, continuous power, and charging lines with the trailer. This version is therefore suitable for horse trailers, bicycle racks, and camping trailers.

Universal electrical systems

This is an electrical kit that is suitable for several types of vehicles. The cables are connected to the tail lights of the towing vehicle using cable connectors. No plugs are included. The cables are long enough for most types of vehicles (exception: platform trucks).

Vehicle-specific electrical systems

These electrical kits are specially matched to different vehicle types. The connections are made using compact plugs which can be connected to the corresponding plugs of the vehicle's tail lights. The cables are sufficiently long for the given type of vehicle.


The Tronic electrical kit has been specially developed by Westfalia and only requires wiring to be made at the tail end of a vehicle. Malfunctions in the trailer turn signal system are indicated by an increased flashing rate of the turn signal indicators in the vehicle.
The advantages are as follows:

  • Universally applicable
  • Wiring only required at tail end of vehicle when a suitable continuous positive signal is available
  • No modifications necessary to dashboard
  • Disassembly of steering wheel (with or without airbag) not necessary.
  • Plugs for control units with secondary locking mechanism (typical OE standard)
  • Sockets with screw connection, i.e., max. diameter of bore hole on vehicle only D = 17 mm
  • Option für seitlichen Kabeleingang an der Steckdose, d.h. für alle am Markt befindlichen Anhängekupplungen mit klappbarem Steckdosenhalter geeignet
  • Option for lateral cable inlet on socket, i.e., suitable for all currently available trailer couplings with foldable socket holder.
  • Complies with current KBA (Kraftfahrtbundesamt) requirements in Germany
  • Includes disabling function for acoustic parking system
  • Disabling function for rear fog lights integrated in control unit

Westfalia Tronic kits are prepared for axial cable outlets in the standard version. The sockets include a break-off area for a lateral cable outlet. This can be broken off when necessary and closed again using a special seal.