Marker lights with indicator function on small trailers: regulations, tips and wiring diagrams

The demand for marker lights with indicator function on small trailers is growing. They improve the trailer’s visibility and give it a more professional appearance, provided you connect them correctly and comply with the regulations in your market.

This article focuses on smaller 12V trailers, which in practice are usually O1 and O2 trailers. Below, you will first find the practical connection options with a scheme, followed by the plug-&-play options and, finally, the regulations for each vehicle category. For heavier O3 and O4 trailers, please refer to our blogs on trailer lighting and truck and semi-trailer lighting.

Why sequential side lighting is becoming increasingly popular

Demand for flashing side marker lights is on the rise. This is hardly surprising. This solution gives a trailer a modern look, but above all contributes to improved visibility on the road. As a result, the vehicle stands out more clearly to other road users, for example when turning, merging or manoeuvring.

Vehicle builders and end-users are also increasingly asking for neater and smarter lighting solutions. Marker lights with an indicator function tie in well with this, provided the application complies with the regulations and is connected without fault.

Do you often work on safety and visibility on trailers? If so, you might also find our article on fitting additional reversing lights of interest.

Heavier O3 and O4 trailers are subject to different lighting requirements than smaller O1 and O2 trailers. That is why, in this article, we are focusing primarily on the lighter segment and the practical connection aspects of its installation.

Connecting marker lights with indicator function

Would you like to fit marker lights with indicator function on a small trailer? There are two common ways to connect them. Which solution is most suitable depends on the trailer’s construction, the lighting used and the desired level of plug-&-play mounting.

Option 1: via extension cable and control unit

This wiring diagram shows an example of marker lights with indicator function via a control unit. Here, the indicator and position light signal are tapped in a controlled way. That makes this solution suitable for applications where you want a neat and interference-free circuit.

This example uses a 7-PIN connector, an extension cable and SuperSeal connections for input and output. This allows you to surface mount the function neatly and reduce the risk of interference.

* Wiring diagram for marker lights with indicator function via control unit

Option 2: directly via multifunctional rear lights

Do you want to connect marker lights with indicator function in a simple and clear way? Then a multifunctional rear light with multiple SuperSeal connections is an efficient solution. You can connect multiple functions from one central unit, without separate branches or extra cabling.

• Flashing side lighting
• Side marker lights
• Licence plate light
• Third brake lamp
• Reversing worklight

This approach saves time on the production floor and keeps the installation straightforward. For vehicle builders and OEMs, this is often a major advantage.

Consider, for example, solutions within the VC 2000 or VC 6000 series, with built-in control unit and multiple SuperSeal connections.

* Wiring diagram of marker lights with indicator function via a multifunctional rear light. VC 2000 series on the left and VC 6000 series on the right.

Plug-and-play solutions with complete wiring harnesses

At TRALERT®, a lot revolves around smart simplicity. That’s why we offer complete plug-&-play lighting solutions that save you time when fitting lights to trailers. Fewer individual steps mean less chance of error and quicker mounting.

Whether you work with a standard wiring harness or a customised solution for your vehicle construction project, clear surface mounting makes marker lights with indicator function easier to reproduce.

Fully canbus compatible

Marker lights with indicator function must work seamlessly with the rest of the lighting system. The side lighting must be able to operate both continuously and in synchronisation with the indicators, without error messages or interference. This is why CAN bus compatibility is a key consideration in many modern applications.

Regulations for blinking marker lights with indicator function

Anyone wishing to fit marker lights with indicator function to a trailer must first comply with the relevant regulations. The regulatory framework for this is ECE R48 (Revision 13, December 2024). Since 1 January 2025, marker lights with indicator function have been compulsory for new O3 and O4 trailers, whilst different requirements apply to O1 and O2 trailers. This is precisely why it is important to carefully consider the vehicle category for which you are building and the market in which the vehicle will be authorised.

In this context, it is important to distinguish between two distinct stages: European type approval in accordance with ECE R48 and the regulations that apply once a trailer has been registered.

• O1 trailers (up to and including 750 kg) and O2 trailers (over 750 kg and up to and including 3,500 kg): under European type approval in accordance with ECE R48, marker lights with indicator function are not permitted at the time of approval. In the Netherlands, a different regulation applies following approval (Article 5.12.64(2) of the Vehicle Regulations): the side marker lights may flash in sync with the indicators on the same side of the vehicle. For other markets, the national legislation of the country in question applies.
• O3 trailers (3,500 kg to 10,000 kg) and O4 trailers (over 10,000 kg): from 1 January 2025, marker lights with indicator function will be compulsory for newly registered vehicles. Existing trailers do not need to be modified.

For more general lighting requirements on O3 and O4 trailers, please refer to our articles on the rules for trailer lighting and truck and semi-trailer lighting.

Bespoke solutions for vehicle builders

Are you a vehicle builder looking for a suitable solution for marker lights with indicator function on small trailers? Then it all starts with choosing the right cabling, control unit and rear lights, tailored to your vehicle bodywork. We’d be happy to help you find a solution that suits your vehicle bodywork, cabling and preferred installation method.

• Technical support and schemes
• Mounting and demonstration videos
• Engineering support for customisation

See also our page on ECE standards and legislation for further background on regulations and vehicle lighting.

Frequently asked questions

What are marker lights with indicator function?

Marker lights with indicator function consist of side marker lights that operate in sync with the trailer’s indicator. This can improve the vehicle’s visibility, provided the application complies with the relevant regulations.

Are marker lights with indicator function compulsory for all trailers?

No. Different regulations apply to small O1 and O2 trailers than to heavier O3 and O4 trailers. That is why it is important to always check the vehicle category first.

How do I connect marker lights with indicator function to 12V or 24V?

This can be done, for example, via a control unit or via a multifunctional rear light with suitable connections. Which method works best depends on the vehicle body and the desired solution.

Is a canbus control box always necessary?

No, not always. In modern vehicles, a control box or CAN bus solution does help to prevent error messages and ensure signals are processed correctly. This often makes the installation more reliable.

How does co-flashing side lighting relate to ECE R48?

ECE R48 forms an important basis for the positioning and operation of vehicle lighting. Whether marker lights with indicator function are suitable for a specific application depends on the vehicle category and the design of the lighting system. Read more on our page about ECE R48.