Reverse Lights: How Many, Reversing Light Bulbs, Law and MOT
A reverse light is a white lamp that comes on in reverse gear. How many reversing lights a car has, W16W and P21W bulbs, UK law and the MOT rules.
In this guide
A reverse light (reversing light) is a white lamp at the back of a vehicle that switches on automatically when you select reverse gear. It lights the ground behind you and warns pedestrians and other drivers that you are about to reverse. A car has 1 or 2 reverse lights: at least 1 is required, and no more than 2 are normally allowed.
This guide covers how a reverse light works, how many a vehicle needs, the UK rules under the Road Vehicles Lighting Regulations 1989 (RVLR) and the MOT, the bulbs reverse lights use, LED upgrades, and the extra points that apply to tractors and trailers.
What Is a Reverse Light and How Does It Work
A reverse light is defined in RVLR as a lamp used to illuminate the road to the rear of a vehicle for the purpose of reversing. It does 2 jobs:
- Lighting: it throws white light onto the ground behind the vehicle so the driver can see where they are going when reversing at night.
- Warning: white light from the back of a vehicle tells everyone nearby that it is in reverse or about to move backwards.
The reverse light is switched by a reverse light switch on the gearbox. On a manual gearbox this is usually a small plunger switch screwed into the gearbox casing, which closes when the selector moves into reverse. On automatics and many modern cars, the gear selector position is read electronically and the body control module switches the lamps. Either way, it is automatic: there is no dashboard switch for a standard reverse light.
The reverse light is always white. All the other rear lamps (tail lights, brake lights and rear fog lamps) are red, and the indicators are amber, so a white light at the back stands out.
How Many Reverse Lights Does a Car Have
A car has either 1 or 2 reverse lights. The MOT requires at least 1, and RVLR allows no more than 2 on a normal car or van. Most modern cars have 2, one in each rear cluster. Some cars have only 1, usually on the nearside, mirrored by a single rear fog lamp on the offside in a matching cluster.
| Vehicle | Reverse lights allowed |
|---|---|
| Car, van or other vehicle up to 6 m long | 1 or 2 |
| Bus, or a non-passenger vehicle over 6 m long | Up to 4 (all to the rear, or 2 to the rear and 1 on each side) |
| Vehicle tested under the MOT (first used from 1 September 2009) | At least 1 must be fitted and work |
So if you are wondering whether you need 2 reverse lights: no. One correctly fitted, working reverse light is enough. But if your car was built with 2, both need to work to pass the MOT (see below).
UK Legal Requirements for Reverse Lights
Reverse lights are covered by RVLR Schedule 14. Since an amendment that took effect on 20 May 2018, RVLR treats a reversing lamp as obligatory on a motor vehicle with 3 or more wheels that is required to have one by vehicle type approval rules, and that obligatory lamp must meet paragraph 6.4 of UN ECE Regulation 48. In practice, this covers modern cars, vans and lorries, which have been built with reverse lights for decades.
Colour
White only. A reverse light with a tinted lens or a coloured bulb that changes the light is illegal and a major MOT defect.
Approval Mark and the 24W Limit
A reverse lamp on a motor vehicle first used on or after 1 April 1986, or a trailer manufactured on or after 1 October 1985, must carry an approval mark (an E-mark). For lamps without an approval mark (on older vehicles), the total wattage of any one lamp must not exceed 24W. That is why reverse light bulbs are 16W or 21W, not the 55W or 60W of a headlamp bulb. Approved lamps have no wattage figure in RVLR because their light output is controlled by the approval itself.
Position
ECE Regulation 48 sets the mounting height of a reverse lamp at 250 mm to 1,200 mm above the ground, facing rearwards. The lamp must light only when reverse gear is engaged (and the ignition is on).
Side-Mounted Reversing Lamps
Where reversing lamps are fitted to the sides of a long vehicle, RVLR adds 3 rules: they must not light unless the front and rear position lamps are on, they must be switched by a single manual switch that does nothing else, and they must switch off automatically if the vehicle moves forward at 10 km/h or more.
Reverse Lights and the MOT
The MOT inspects reverse lights on vehicles first used on or after 1 September 2009. On those vehicles, a reverse light that does not work is a major defect, which means an MOT fail.
| MOT check | Defect | Category |
|---|---|---|
| Condition and operation | A reversing lamp inoperative | Major (fail) |
| Condition and operation | Lens defective | Major (fail) |
| Security | Lamp not securely attached / likely to become detached | Minor / Major |
| Compliance | Colour (not white) or position not as required | Major (fail) |
| Switching | Lamp does not come on in reverse, or does not go off when reverse is deselected | Major (fail) |
Older guidance (including earlier versions of this page) said a dead reverse light was only an advisory. That is not right for vehicles in scope: the current MOT inspection manual lists “a reversing lamp inoperative” as a major defect, with no exception for a second lamp that still works. Vehicles first used before 1 September 2009 do not have their reverse lights inspected at all.
For a step-by-step fault guide and more on the MOT rules, read our guide to reverse lights not working.
Reverse Light Bulb Types
Most reverse lights use either a W16W (921) wedge bulb or a P21W (382) bayonet bulb. Some use a W21W (582) wedge bulb, and many newer cars have LED reverse lamps built into the cluster.
| Bulb | Trade code | Base | Wattage | Typical use |
|---|---|---|---|---|
| W16W | 921 (also 955; T15 shape) | W2.1×9.5d capless wedge | 16W | Many modern cars, especially compact clusters |
| P21W | 382 | BA15s bayonet | 21W | Older cars, vans, tractors and trailer lamps |
| W21W | 582 | W3x16d capless wedge | 21W | Some modern European cars |
| LED (integrated) | None | Built into the lamp | A few watts | Many cars from the 2010s, LED combination lamps |
“T15” is a name many sellers, especially LED bulb sellers, use for the same capless wedge size, so a box labelled T15, 921 or W16W usually fits the same holder. Our guides to W16W 921 bulbs and P21W 382 bulbs explain each one in detail, and you will find replacements in our standard miniature bulbs range.
How to Find Your Reverse Light Bulb
Check the vehicle handbook first. If you do not have it, take out the old bulb: the code is usually printed on the metal base or the glass. A wedge bulb with no metal cap is a W16W or W21W (the W21W is noticeably larger); a bulb with a metal cap and 2 level pins is a P21W.
Upgrading to LED Reverse Lights
LED reverse lights can give a whiter, brighter light behind the vehicle and last far longer than a filament bulb. There are 2 ways to do it, and they are not equal.
Complete LED Reverse Lamps
A complete LED reversing lamp with an E-mark (look for the AR marking on approved reversing lamps) is a legal, approved lamp. This is the right way to add or upgrade reverse lights on a trailer, tractor, van or older vehicle. Browse our reverse lamps for universal fitments.
LED Replacement Bulbs
LED bulbs that plug into a holder designed for a W16W or P21W are a grey area. Most are not type approved as a substitute for the filament bulb, so strictly the lamp is no longer as it was approved. The MOT checks that the reverse light works and shows white; it does not have a specific “light source not compatible” defect for reverse lights as it does for headlamps. Choose a pure white bulb, and check the beam is not scattered in a way that dazzles.
CANbus Warnings
Many modern cars monitor bulb current. An LED bulb draws so little that the car may report a “bulb failure” or the light may flicker. CANbus-compatible LED bulbs include a load resistor or driver to stop this. If you fit an add-on resistor, mount it on metal away from plastic, because it gets hot.
Common Reverse Light Faults
A reverse light that will not work usually comes down to 1 of 4 things: a blown bulb, a blown fuse, a faulty reverse light switch, or a wiring fault.
- One light out: almost always the bulb or a corroded holder.
- Both lights out: usually the fuse or the reverse light switch on the gearbox.
- Lights stay on all the time: a reverse switch stuck closed, or a short in the wiring.
- Lights flicker: a poor earth, a loose holder, or an LED bulb on a CANbus car.
The quick test for the switch is to unplug it and bridge the 2 terminals in the plug with a fused jumper wire (ignition on, engine off). If the reverse lights come on, the switch is faulty. The reverse lights not working guide linked above walks through each check in order.
Reverse Lights on Trailers and Tractors
Trailers
RVLR does not list a reversing lamp as obligatory on a trailer, although many newer trailers are built with one and a reverse light is a real help when backing a trailer into a yard or onto a ramp at night. If a reverse lamp is fitted, it must be white and approved.
The reverse light feed comes through the towing socket. On a 13-pin socket (ISO 11446), pin 8 carries reverse. A standard 7-pin 12N socket has no reverse light pin; the 7-pin 12S auxiliary socket can carry one, but its pin use varies, so check the wiring. Upgrading the tow vehicle and trailer to 13-pin is the neatest answer. Browse our 13-pin plugs and sockets.
Tractors
Many modern tractors have rear lamps with a reverse function or rear work lights that can be switched on when reversing. Older tractors often have none. Adding reversing lights to a tractor raises its own questions about wiring to the shuttle or reverse switch, and about using work lights on the road. See our guide to tractor reversing lights for the details.
Frequently asked questions
How many reverse lights does a car need?
At least 1. RVLR allows up to 2 on a normal car or van (up to 4 on buses and non-passenger vehicles over 6 m long). Many cars have 2, some have 1.
Is a reverse light an MOT failure?
Yes, on vehicles first used on or after 1 September 2009. A reversing lamp that does not work, shows the wrong colour or does not switch with reverse gear is a major defect. Older vehicles do not have their reverse lights inspected.
What bulb is a reverse light?
Usually a W16W (921) wedge bulb or a P21W (382) bayonet bulb, sometimes a W21W (582). Check the handbook or the old bulb, because the bases are not interchangeable.
What colour must reverse lights be?
White. Any other colour is illegal and fails the MOT.
Why are both my reverse lights not working?
When both go at once, suspect the fuse or the reverse light switch on the gearbox before the bulbs. Check the fuse first, then bridge the switch plug to test the switch.
