Retrofitting towbars
A towbar turns your vehicle into a real workhorse – whether for a DIY store trailer, a caravan or a bike rack. Retrofitting is often easier than you think, but requires technical know-how, the right choice of components and a close look at the legal requirements. At Electronicx, everything revolves around high-performance vehicle electronics – from AGM and EFB batteries to LiFePO4 storage and smart tyre pressure monitoring systems – but as a service-oriented supplier we know: safe trailer driving starts with a professionally fitted and electrically cleanly integrated towbar. In this comprehensive guide, you will learn step by step what to look out for, which towbar types exist, how the electrical connection is made and how Electronicx helps you make your trailer operation more reliable.
Why retrofit a towbar?
Whether private or commercial – the reasons for retrofitting are many. The van for the next move, the caravan for the holiday trip or regular garden waste: with the right towbar, your car becomes a multi-talent. Some vehicles already leave the factory with a factory-fitted trailer preparation, but many models do not. The good news: almost every modern vehicle can be equipped with a retrofit kit, provided the permissible towing capacity (noted in the vehicle documents) allows sensible use. Registration in the vehicle registration document and an inspection by a testing organisation (TÜV, DEKRA etc.) ensure legal certainty. And anyone who values a stable on-board electrical system benefits from an intact 12 V supply – an area where a high-quality car battery makes the difference.
Overview of available towbar types
Before you start retrofitting, it is worth taking a close look at the different designs. Each has its advantages and disadvantages – depending on the intended use, budget and visual preference.
Fixed (rigid) towbar
This variant is bolted firmly to the vehicle frame and cannot be removed. It stands out for its high robustness and low susceptibility to wear. The ball head (diameter 50 mm) is permanently mounted. Disadvantage: the ball head always remains visible and can get in the way during parking bumps. Vehicles with rear parking assist or sensitive bumper designs benefit from other solutions. The permissible nose weight here is usually 75–100 kg, depending on the vehicle type.
Detachable towbar
The ball head is released via a mechanism and can be stowed in the boot when not in use. There are two subtypes:
- Horizontally detachable: The ball head is pulled sideways out of the mounting slot. Simple handling, sometimes without tools.
- Vertically detachable: A retraction mechanism (often retrofittable) pulls the ball head upwards under the bumper. Visually almost invisible, but more expensive and more complex to install.
The typical towing capacity ranges from 1,500 kg to 2,500 kg (for mid-range estates), and the nose weight is also 75–100 kg. The electrical contact for the trailer lighting is provided via a socket adapter (7‑pin or 13‑pin).
Swan-neck towbar
Very convenient: the ball head is swivelled under the bumper by lever or electrically. No manual attachment required – ideal for frequent users. The space required behind the vehicle remains minimal, and the appearance is tidy. However, electric swivelling towbars require sufficient on-board voltage and a stable battery so that the mechanism works reliably even after long periods of standing.
The following table summarises the essential features:
| Towbar type | Detachable | Max. typical towing capacity (car) | Installation effort | Material cost (approx.) | Ideal for |
|---|---|---|---|---|---|
| Fixed towbar | No | 1,800–2,500 kg | Medium | 150–250 € | Frequent, robust use |
| Detachable (horizontal) | Yes, manual | 1,500–2,200 kg | Medium to high | 200–350 € | Appearance + occasional use |
| Detachable (vertical) | Yes, manual | 1,600–2,300 kg | High | 300–500 € | Invisible appearance, convenience |
| Swivelling (manual/elec.) | Yes, swivelling | 1,500–2,200 kg | Very high | 400–800 € | Demanding design, frequent users |
Note: All prices are approximate values for the towbar system without installation. Labour costs vary greatly by region.
Check the requirements for retrofitting
- Check the vehicle registration document: The registration certificate Part I (fields O.1 and O.2) lists the technically permissible braked/unbraked towing capacity as well as the maximum nose weight. Only these values may be used.
- Vehicle type and general conditions: Not every car is designed for trailer operation. In particular, small cars or pure electric vehicles with a low permissible towing capacity require special solutions. Leased vehicles often require separate approval from the lessor.
- Electrical preparation: Many vehicles already have a 12‑V permanent positive and CAN‑bus lines prepared in the boot. When retrofitting, you should look for a vehicle-specific electrical kit (7‑pin or 13‑pin) that controls lamp monitoring, trailer stability programme (TSC) and reversing assist systems without errors.
- Space for the towbar substructure: The cross member or body mounting must offer sufficient stability. Some vehicles require a special reinforcement plate, which is included in the retrofit kit.
- Cooling and on-board electrical system: Trailer operation places additional demands on the vehicle's cooling (engine, transmission) and on the on-board electrics. A powerful battery – preferably a cycle-resistant AGM or EFB battery with a cold cranking current of 680–800 A (CCA) – is advisable in order to avoid voltage drops during starting. Electronicx offers suitable solutions for this with free DHL shipping within Germany.
Installation types: workshop or DIY?
Whether you do it yourself or commission a specialist workshop depends on your skill and the complexity of the vehicle.
Professional retrofitting in a workshop
Advantages: the workshop handles the complete mechanical and electrical installation, carries out the required coding via diagnostic tester and, on request, arranges the TÜV approval and the document entry. The costs are between 500 and 1,000 euros depending on the vehicle model and towbar type (including material). A reputable workshop works with vehicle-specific, ABE‑approved retrofit kits and tells you in advance how many labour hours will be required (usually 2 to 4 hours).
DIY: retrofitting a towbar yourself
Anyone with access to a vehicle lift, a torque wrench and a basic understanding of vehicle technology can carry out the mechanical installation themselves. Bear in mind: on modern vehicles with CAN bus and complex control units, a special cable set with a control module ("CAN bus adapter") is essential. This module picks up the signals from the vehicle electrical system and controls the trailer lighting completely separately from the vehicle lighting in order to avoid error messages. An incorrectly connected 12 V permanent live can interfere with the electrical system and lead to premature battery failure – a scenario that can be managed with a cycle-resistant AGM battery. Even in Hamburg or Munich, a reliable starter battery is worth its weight in gold – feel free to get in touch!
Electrical connection step by step
The electrical retrofit kit generally includes a socket holder (under the bumper or in the tow bar carrier), a 7-pin or 13-pin plug and the vehicle wiring harnesses. In addition to the lighting, the 13-pin plug also provides a permanent live (pin 9) and an ignition live (pin 10) – ideal for charging a battery in the trailer or operating a manoeuvring aid. On vehicles with start-stop automatic, the control module must send feedback to the energy management system so that the engine start remains assured. After installation, the system usually has to be taught in with a diagnostic tester (control unit coding). Without successful coding, the trailer lighting may remain non-functional or bombard the dashboard with warning lights.
Legal requirements – ABE and registration obligation
Every retrofitted tow bar must have a general operating permit (ABE) or an EC approval. The ABE lists the vehicle types, installation instructions and the trailer loads to be achieved. After installation, the tow bar must be inspected without delay by an officially recognised testing organisation. If installation is correct, the inspector will note the change in the vehicle documents. Without this entry, the operating permit expires – the consequence is an expensive fine and the threat of deregistration. Installation workshops with the appropriate certification (e.g. a KÜS centre) can carry out the inspection directly.
Cost factors in detail
- Retrofit kit (mechanical): 150–500 euros (fixed to electrically swivelling). Vehicle-specific kits from brand manufacturers such as Westfalia, Oris or Bosal are in the upper range.
- Electrical kit (7-pin / 13-pin): 50–150 euros. CAN bus-capable kits with control module are more expensive, but mandatory on newer vehicle generations.
- Labour: 80–120 euros per hour. Total effort usually 2–4 hours.
- Additional inspection costs: around 40–70 euros (TÜV, DEKRA, KÜS).
- Battery upgrade: If the factory battery reaches its limits with frequent trailer operation, it is worth investing in a reinforced AGM or EFB battery (from around 120 euros).
You can obtain comprehensive advice – including on high-performance electrical system components – from us. Our customers in Munich, for example, appreciate the fast delivery of high-quality car batteries for Munich and the surrounding area.
Why the right battery is crucial
Trailer operation places a double load on the vehicle electrics: additional consumers (trailer lighting, cool box, manoeuvring aid) draw on the battery when the engine is switched off, while the start-stop system intervenes more frequently in city traffic (e.g. in Cologne or Stuttgart). A conventional starter battery is only designed to a limited extent for such cycles. Thanks to glass mat technology, AGM batteries offer a cycle resistance 3 to 4 times higher than flooded batteries, deliver a stable cold cranking current (EN standard, e.g. 760 A CCA) and recover more quickly after deep discharge. Especially for drivers who regularly commute between Dortmund and Düsseldorf and tow a trailer, this is a safety bonus. You can find out more about the specific requirements in the region on our page for Dortmund.
Don't forget tyre pressure and safety
Trailer operation increases the risk of gradual pressure loss due to higher loads and longer standing times. A tyre pressure monitoring system (TPMS) is indispensable for the safety of all road users – for the towing vehicle and, where available, even for the trailer. Electronicx carries a wide range of sensors pre-programmed for your vehicle. Incorrect tyres not only lead to increased fuel consumption but also to unstable handling with a trailer. Browse our Sensor-Tpms category and find the right sensor for your rim. For users who want to set up the entire system from scratch, we recommend taking a look at Tire Pressure Monitoring System Sensor Tpms.
FAQ – Frequently asked questions about retrofitting tow bars
Can I fit a tow bar myself?
Yes, mechanically this is possible on some vehicles with DIY skills. On modern vehicles, however, the electrical part often requires a CAN bus adapter and coding with a diagnostic device. Without these, the trailer lighting can fail or the vehicle electrical system can be disrupted. If in doubt, have it fitted by a specialist workshop.
Does the tow bar have to be registered?
Yes. Every retrofitted tow bar with an ABE must be inspected by an official testing organisation and entered in the vehicle documents. If the entry is missing, fines and the loss of the operating permit may follow.
What is the difference between a 7-pin and a 13-pin connector?
The 7-pin connector only transmits the lighting (indicators, brake light, sidelights). That is enough for small trailers. The 13-pin connector additionally offers permanent live (e.g. for interior lighting or battery charging), ignition live and a separate reversing light circuit. For caravans or horse trailers, 13-pin is the better choice.
Which tow bar fits my car?
The vehicle data (model, key number, year of manufacture) determine the right retrofit kit. Manufacturers such as Westfalia or Oris offer online configurators. Make sure the ABE number is correct and matches your vehicle.
How high is the permissible towing capacity?
Take the values from the Zulassungsbescheinigung Teil I (fields O.1 for braked trailers, O.2 for unbraked). The load that can actually be used is also limited by the tow bar fitted – the lowest value applies.
Does the tow bar affect car insurance?
Yes, you must report the change to your insurer. A retrofitted tow bar counts as increasing the value, but may under certain circumstances affect the partial comprehensive cover. Ask your insurer before converting.
Can my electric car tow a trailer?
Some electric cars have a factory-fitted tow bar and a notable towing capacity (e.g. Tesla Model Y 1,600 kg). Many pure electric cars, however, are not approved for trailer operation. Check the manufacturer's specifications and the entry in the vehicle registration document.
Do I need a stronger battery for a retractable tow bar?
An electric retractable tow bar briefly requires high currents (10–20 A), which can put a strain on the battery in start-stop vehicles. An AGM battery with sufficient reserve capacity (RC > 120 minutes) is recommended and is also offered by Electronicx.