Lights, reflectors and electrical MOT failures
The single most common MOT failure area – and usually the cheapest to fix. In April–June 2026 lamps and electrical equipment caused failures in around one in ten of all tests.
Checked against the MOT inspection manual and GOV.UK guidance · Updated November 2026
What the tester checks
Section 4 of the MOT inspection manual covers every lamp, reflector and electrical item. The tester checks each lamp is present, secure, works, is the right colour, isn't seriously damaged and that the switch and tell-tale (where fitted) work. Headlamps are also checked for aim with a beam-setting machine.
- Headlamps – dipped and main beam, aim, beam pattern, colour, lens condition, levelling and cleaning devices where fitted
- Front and rear position (side) lamps
- Stop lamps – including the high-level centre brake light
- Direction indicators and hazard lamps – including side repeaters, flash rate and tell-tale
- Rear fog lamp – at least one on cars first used from 1 April 1980, with a working tell-tale
- Reversing lamps – cars first used from 1 September 2009
- Front fog lamps and daytime running lamps – cars first used from 1 March 2018
- Rear registration plate lamp, rear reflectors
- Battery – secure, not leaking
- Wiring – secure, not damaged or likely to short
- Trailer electrical socket, if a tow bar is fitted
Common lighting failures
| Defect found | Usual category |
|---|---|
| Headlamp, brake or indicator lamp not working | Major |
| Both stop lamps not working | Dangerous |
| Headlamp aim too high or too low | Major |
| Light source incompatible with the headlamp (e.g. LED or HID bulb in a halogen unit) | Major |
| Lamp emitting the wrong colour (e.g. blue-tinted, tinted lens covers) | Major |
| Lens badly damaged so light is affected, or missing | Major |
| Indicator flashing faster or slower than 60–120 times per minute | Major |
| Rear fog lamp tell-tale not working | Major |
| One number plate lamp out (where two fitted) | Minor |
| Battery insecure or leaking | Major |
| Wiring insecure and likely to be damaged | Minor |
Headlamp aim
Headlamp aim is the lighting failure drivers most often can't explain. It happens after a headlamp unit or bulb is replaced, after front-end accident damage, or when the levelling motor fails (the adjuster on the dashboard does nothing). A beam that's too high dazzles oncoming drivers; too low and you can't see. Most garages can re-aim headlamps in a few minutes for a small charge; a failed levelling motor or a headlamp unit with broken mounting lugs costs more.
LED and HID conversion bulbs
Fitting LED or HID (xenon) "upgrade" bulbs into headlamps designed for halogen bulbs is a common failure since the 2018 MOT changes. The reflector or projector is designed around a halogen filament; a different light source scatters light and dazzles other drivers. The tester will fail a light source that's incompatible with the headlamp unit, whatever the packaging said about being "road legal". Refit the correct halogen bulbs.
Cloudy or yellowed headlamp lenses
Oxidised plastic lenses reduce output and scatter the beam. Mild clouding is usually an advisory; if it's bad enough to affect the beam pattern it can fail. A restoration kit (£10–£25) or a professional polish fixes most.
Repair costs
| Repair | Typical cost | DIY? |
|---|---|---|
| Replace a standard bulb (indicator, brake, side, plate) | £5–£20 | Yes, usually |
| Replace a halogen headlamp bulb | £10–£40 | Often – some cars need bumper removal |
| Headlamp re-aim | £10–£30 | No – needs beam setter |
| Xenon/HID bulb | £60–£180 | Sometimes |
| Headlamp unit (complete) | £120–£600+ | Sometimes |
| Headlamp levelling motor | £60–£200 | Sometimes |
| Rear lamp cluster | £40–£200 | Usually |
| Battery | £80–£180 | Yes on most older cars |
| Wiring fault diagnosis and repair | £60–£250 | Depends |
Typical UK independent garage prices including parts, labour and VAT, 2026. Main dealers and premium/4x4 vehicles cost more.