Mandatory towing lights: Everything you need to know

Towing a poorly lit trailer isn't just a real accident risk from reduced visibility — it's also one of the most common reasons for a fine or an on-the-spot prohibition at a roadside check, or for a failed periodic inspection. Trailer lighting rules are built on UN/ECE Regulation No. 48 (installation of lighting and light-signalling devices), carried into national law through vehicle type-approval — and the detail doesn't always match what's commonly assumed. This guide covers what's mandatory, what stays optional depending on weight and dimensions, and which connector you need. If you're still deciding which trailer type suits your bike, you can check that first in what types of motorbike trailers are there.

Why is lighting mandatory on a trailer?

A hitched trailer partly or fully blocks the towing vehicle's rear lights: without its own lighting, other road users can't tell whether you're braking, turning, or — at night — judge the distance to you. Driving without the required lighting is an offence, and at inspection it's a fault that can fail the vehicle.

What lights must a trailer have?

Not every trailer needs the same lighting: the rules differ by maximum authorised mass (MAM) and by dimensions (width and length). Here's what's currently required:

Mandatory on every trailer, regardless of size

• Rear position (tail) lights (red), at least two, one on each side.
• Stop lights, at least two, which light up when the brake pedal on the towing vehicle is pressed.
• Rear indicators, at least two, amber.
• Number plate light, illuminating the trailer's own rear plate (where fitted) or the towing vehicle's.
• Rear reflectors, red and triangular (unlike motor vehicles, where triangular reflectors aren't allowed).

Mandatory only above certain dimensions

• Front position light (white): mandatory if the trailer is wider than 1.60 m.
• End-outline marker lights: mandatory if width exceeds 2.10 m.
• Side marker lights: mandatory on trailers longer than 6 metres, for first registrations from 26 July 1999 onward.

Optional, even if very common

• Rear fog lamp: UN/ECE Regulation No. 48 classes it as optional on trailers, regardless of category (O1, O2, O3 or O4). In practice, most trailers fitted with a 13-pin connector carry one anyway; if fitted, it must comply with Regulation No. 38 (the specific type-approval for rear fog lamps). "Optional" doesn't mean "not allowed" — if it comes fitted from the factory, it has to work correctly and can't be disconnected.
• Reverse light: here the deciding factor is weight, not manufacturer preference. It's optional on category O1 trailers (MAM 750 kg or below) and mandatory on category O2, O3 and O4 trailers (MAM over 750 kg) first registered from 10 July 2011, under Regulation No. 48 read with Regulation No. 23.

A note on accuracy: the rear fog lamp is often claimed to be mandatory above 750 kg, by analogy with the reverse light. Under the text of UN/ECE Regulation No. 48, the two are regulated independently, and only the reverse light is weight-conditioned; the rear fog lamp stays optional on trailers regardless of mass. For an older trailer, or if your specific case is unclear, your vehicle's registration document or a direct check with your national testing authority is the most reliable way to confirm it. National implementation of Regulation No. 48 can also carry local variations — worth double-checking against your country's own road traffic or vehicle lighting regulations if anything here looks off for your market.

The connection: connectors and compatibility

The electrical connector between the towing vehicle and the trailer isn't a minor accessory — it's what allows all these lights to receive a signal at all.

• 7-pin connector (ISO 1724): covers the basic functions — position, brake, indicators, rear fog lamp and number plate light. This is the standard on light trailers, including most motorbike trailers.
• 13-pin connector (ISO 11446): adds independent circuits for each indicator, the reverse light and, in some cases, a permanent supply or battery charging line (useful for trailers with a fridge or interior lighting). This is what you need if your trailer has a reverse light, or if you want that option available.

If your towing vehicle only has a 7-pin socket and the trailer needs 13 (or vice versa), approved adapters exist: rewiring or "bridging" connections yourself isn't allowed, since it can disable safety functions such as anti-snaking or trailer stability control on models fitted with it.

Does the lighting need to be type-approved?

Yes. Any lighting device fitted to a trailer must be type-approved under UN/ECE Regulation No. 48 (currently in its 2019/57 revision, updating the 2007 version), which governs the installation of lighting and light-signalling devices on vehicles and trailers. Approval covers more than the light itself (which in turn must meet its own specific regulation, such as No. 38 for rear fog lamps or No. 23 for reverse lights) — it also covers where and how it's mounted: height above the ground, spacing between lights, visibility angle.

If you change, add to, or modify your trailer's lighting from how it left the factory, that modification needs to be checked at inspection before you drive again; otherwise the trailer stays non-compliant even if the lights "work".

Maintenance

A type-approved lighting system is no use if it doesn't work when it matters. Before any long trip, and periodically:

• Check all six basic functions (position, brake, indicators, number plate, rear fog lamp if fitted, reverse light if fitted) with someone outside the vehicle, or using the reflection in a shop window.
• Check the connector and pins: corrosion and dirt are the most common cause of intermittent trailer lighting faults.
• Replace blown bulbs with identical, type-approved ones; avoid generic LED kits with no CE marking or approval for that specific lamp unit, since they can distort the light pattern and fail inspection.
• Keep the lenses clean: a dirty or hazy lamp loses brightness even with a perfectly good bulb inside.

If youre thinking about buying a trailer for your bike

All of the above applies just the same if the trailer is for carrying a motorbike: the wiring and lighting don't change based on what you're hauling. What does change is that, with a foldable motorcycle trailer, it's worth checking before you buy that the connector, light type and approval are already sorted from the factory, so you don't have to add or change anything afterwards. You can see how that's handled in our range of foldable motorcycle trailers.

Frequently asked questions

Can I tow a trailer without a rear fog lamp?
Yes. Under UN/ECE Regulation No. 48, the rear fog lamp is optional on trailers, regardless of weight. If your trailer doesn't have one fitted from the factory, that's not a fault at inspection.

Does my trailer under 750 kg need a reverse light?
It's not mandatory: category O1 trailers (MAM ≤ 750 kg) keep it as optional. It is mandatory on trailers over 750 kg (categories O2, O3, O4) first registered from 10 July 2011 onward.

Which connector do I need to add a reverse light to my trailer?
The 7-pin connector has no dedicated circuit for that function; you'll need a 13-pin connector (ISO 11446), on both the trailer and the towing vehicle.

Can I fit an LED lighting kit myself?
Yes, as long as the kit is type-approved for that specific lamp unit (a "universal" LED bulb isn't enough), and you declare the modification at your next inspection before driving again. A kit with no CE marking or specific approval is grounds for a fail.

Are the trailer's lights wired separately from the car, or do they share a circuit?
They share the towing vehicle's circuit through the connector (7 or 13-pin): when you brake or indicate in the car, the signal is passed to the trailer over that same wiring. It isn't an independent system with its own battery, except on trailers with extra equipment (a fridge, interior lighting) that can draw a permanent supply through the 13-pin socket.