Trailer reversing lights: legislation and tips

In this article, you will read:

• whether reverse lights are compulsory on your O1 or O2 trailer;
• when a light is officially classified as a reverse light;
• the mounting and wiring requirements that the light must meet;
• Which connector you need and why the operation varies depending on the towing vehicle.

Are reverse lights compulsory on an O1 or O2 trailer?

This depends on the category. According to UN/ECE R48 (para. 6.4.1), reversing lights are mandatory on trailers in categories O2, O3 and O4, and optional on O1. The number of lights depends on the length (para. 6.4.2).

Category	Maximum mass	Up to and including 6,000 mm in length	Longer than 6,000 mm
CategoryO1	Maximummass up to 750 kg	Up to 6,000 mm in length(optional)	Longer than 6,000 mmOptional (rarely relevant)
CategoryO2	Maximummass: 750 to 3,500 kg	Mandatory for lengths up to 6,000 mm¹, 1 additional light permitted	Mandatory for lengths over 6,000 mm², 2 additional lights permitted

Source: R48 para. 6.4.1 (presence), para. 6.4.2.1 (up to 6,000 mm) and para. 6.4.2.2 (longer than 6,000 mm).

Please note: ‘optional’ does not mean that anything goes. A reverse light that you choose to fit to an O1 vehicle must still be type-approved, correctly fitted and only illuminated when reversing. The above requirements are the R48 requirements. If the vehicle in question is an older trailer or is registered in another country, please also check the relevant national regulations.

When is a light considered a reverse light?

A reverse light illuminates the area behind the vehicle and warns other road users that the vehicle is reversing. It is therefore not just any old white light. As a wholesaler of trailer lighting, TRALERT® helps its partners choose the right light. Always check two aspects:

Low	What do you check?	Where can you find that?
Level 1. The light	What should you check?Approved as a reverse light: E-mark with function code AR and approval number	Where can you find this?ECE R23 or R148, marking on the light
Section2. Mounting	What do you check?Position, height, visibility and switching	Where can you find this?ECE R48, paragraph 6.4, plus national regulations of the country of use

A white light without an AR marking does not count as a reverse light, even if it emits a clear light. Furthermore, for type approvals in accordance with the 09 series of R48 (Amendment 6), the light must also be approved in accordance with R23 or R148 in the 00 series or later (para. 6.4.2.3). An approved light is therefore not automatically permitted in every position: the mounting must also be correct.

Mounting requirements for reverse lights in accordance with R48

Section	Requirement	Source (R48)
ComponentColour	EisWit	Source (R48), para. 5.15
ComponentHeight	Requirement: Minimum 250 mm and maximum 1,200 mm above the ground	Source (R48), para. 6.4.4.2
Component Positionalong the length	Requirement: At the rear	Source (R48), para. 6.4.4.3
Component: Visibility (single light)	Specification: 15°up, 5° down, 45° to the left and right	Source (R48)para. 6.4.5.1
Component: Visibility (two lights)	Specification: 15°upwards, 5° downwards, 45° outwards and 30° inwards	Source (R48)para. 6.4.5.1
PartDirection	Requirement: Look behind	Source (R48), para. 6.4.6.1
ComponentCircuit	Requirement: Only when reverse gear is engaged	Source (R48)para. 6.4.7.1

Practical tip: on small trailers, the rear light is often already positioned low down. A combined rear light unit must also be fitted within a height of 250 to 1,200 mm to qualify as a reverse light.

Circuit: the light only comes on when reversing

R48, paragraph 6.4.7.1, stipulates that the reverse light may only be illuminated when reverse gear is engaged and the vehicle is ready to start. If either of these conditions is not met, the light must not come on or remain illuminated.

A trailer does not have its own gearbox. The signal comes from the towing vehicle via the connector, and this is precisely where the differences between vehicles arise.

Which connector do you need for reverse lights?

Small trailers generally operate on 12 Volts. The connector determines whether the reversing signal is available:

Connector	Reversing lights	Connection
13-pin plug(ISO 11446)	ReversinglightYes	Connection: Pin 8 (grey)
7-pin plug(ISO 1724, 12N)	ReversinglightNo	Connection: No PIN for reversing lights

If your O2 trailer has a 7-PIN connector and you wish to connect a reverse light, you will need a 13-PIN connector. A 13-PIN to 7-PIN adapter only transmits the 7-PIN functions, so the reversing signal will still be missing. You can find the full pin diagram in our article on connecting trailer lighting.

Why doesn’t the same trailer work with every towing vehicle? Not every vehicle transmits the reversing signal in the same way. In modern vehicles, the signal is transmitted directly, via a trailer module or via vehicle software. Trailer modules also monitor light status and load, which can sometimes cause LED lighting to display an error message or fail to activate. You can read more about this in our article on CAN bus interference with LED lighting.

Reversing lights not working? Here’s what to check first

The fault rarely lies with the light itself. Check in the following order:

1. Signal: is there voltage on PIN 8 (13-PIN) when reverse gear is engaged?
2. Mass connection: is the mass connection secure and free from corrosion?
3. Connector and ‘ adapter ’: is there a 7-PIN connector or adapter in the circuit? If so, there will be no signal.
4. Cabling and connectors: are there any signs of moisture, loose pins or contact resistance?
5. Vehicle diagnostics: does the towing vehicle display an error message regarding the LED lighting?

You can find further steps in our article ‘Trailer lighting not working’.

What should you look out for when choosing reverse lights?

• Approval: E-mark with function code AR and approval number (R23 or R148). If the reverse light is part of a combination rear light, check that the AR code is marked on that unit.
• Sealing: choose an IP rating suitable for a trailer that is kept outdoors, drives through water and is hosed down.
• Connection: choose a connection method that fits into the 12V wiring harness. You can find more tips in our article on putting together trailer lighting.

Checklist before fitting a reverse light

• What is the category (O1 or O2) and how long is the trailer?
• Does the light have an E-mark with function code AR (R23 or R148)?
• Is the light positioned between 250 and 1,200 mm above the ground, at the rear and facing backwards?
• Does the trailer have a 13-PIN connector, and does the reversing signal come in on PIN 8?
• Have the ground connection, connector and cabling been checked for moisture and contact resistance?
• Have the national regulations of the country of use been checked?

Frequently asked questions

Are reverse lights compulsory on a trailer?

This depends on the category. According to R48 (para. 6.4.1), it is mandatory on O2, O3 and O4 trailers and optional on O1 trailers. You should also always check the national regulations of the country in which the trailer is being used.

How many reverse lights may an O2 trailer have?

For lengths up to and including 6,000 mm, one light is mandatory and a second is permitted (R48 para. 6.4.2.1). For vehicles over 6,000 mm in length, two lights are mandatory and two additional lights are permitted (para. 6.4.2.2).

Can I use a standard white light as a reverse light?

Only if the light is approved as a reverse light (R23 or R148, function code AR) and complies with the mounting and switching requirements of R48, paragraph 6.4. A white light without this approval is not a reverse light.

Does a reverse light work with a 7-PIN connector?

No. The 7-PIN connector (ISO 1724, 12N) does not have a PIN for reversing lights. A 13-PIN connector is required for this, with the signal running via PIN 8.

Do reversing lights work the same on every trailer?

No. The operation varies depending on the towing vehicle, plug configuration, wiring harness, mass and vehicle diagnostics. You should therefore treat a reverse light as a system integration rather than a simple bulb replacement.

What applies to O3 and O4 trailers?

Reversing lights are also mandatory here (R48 para. 6.4.1). The length requirements and the additional side lights are set out in our article on work lights and reversing lights for O3 and O4 trailers.

Please note

This article is a practical guide to UN/ECE R48 and does not constitute legally binding advice. For a definitive assessment, the vehicle category, dimensions, the light’s approval mark, the mounting position and the national regulations of the country of use are decisive.

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Disclaimer:

At TRALERT®, we do our best to keep the information in this article as accurate and up-to-date as possible, including the regulations surrounding vehicle lighting. However, legislation can change regularly, and although we make every effort to implement these changes in a timely manner, it is possible that certain updates or adjustments have not yet been incorporated into this article. We therefore always advise our readers to check the current legislation with their local government or regulatory bodies, especially when it comes to exceptions or specific national regulations. TRALERT® is not liable for any damages or fines resulting from outdated or incomplete information in this article.

If in doubt, always contact the competent authority to ensure that your vehicle meets all legal requirements.