Quick answer
A number plate light can fail an MOT if it does not work, is missing, is insecure, has a broken lens, or does not illuminate the rear registration plate clearly.
This is usually a simple fix. A blown bulb, dirty lens, corroded holder or poor connection is often the cause.
When number plate lights can fail MOT
Bulb not working
No light output from one or more rear plate lamps.
Plate not visible
The rear registration cannot be clearly illuminated.
Broken lens
A missing or damaged lens can affect light output or water resistance.
Loose lamp unit
The lamp should be secure and not hanging loose.
Water ingress
Moisture can damage bulbs, holders and contacts.
Wiring fault
Broken wires, poor earths or corroded connectors can stop the lamp working.
Common reasons number plate lights stop working
The most common cause is a failed bulb. On older cars, corrosion in the bulb holder or damaged wiring near the boot lid is also common.
Some newer vehicles use sealed LED units. If the LED section fails, the complete lamp unit may need replacement.
What to check before the MOT
1. Turn lights on
Switch on sidelights or headlights and inspect the rear plate lights.
2. Check both lamps
Some cars use two bulbs, so make sure the full plate is lit.
3. Clean the lenses
Mud and dirt can reduce brightness and visibility.
4. Inspect for cracks
Broken housings can let water into the lamp.
5. Replace failed bulbs
This is often quick and inexpensive.
6. Check the plate too
A dirty, faded or damaged number plate can also fail.
Usually an easy repair
Number plate light faults are often among the simplest MOT issues to fix. Replacing a bulb, cleaning contacts or fitting a new lens may solve the problem quickly.
If the bulb keeps failing or the light flickers, check for water ingress, damaged wiring or a poor earth connection.
Related MOT lighting guides
Frequently asked questions
Will one number plate bulb out fail MOT?
It can if the rear plate is not properly illuminated.
Is it usually an easy fix?
Yes, it is often just a bulb, holder or connection issue.
Do LED number plate lights fail too?
Yes. LED units can fail and may need replacement as a complete unit.
Can dirt cause an MOT issue?
Yes, heavy dirt can reduce plate visibility and should be cleaned.
Should I check before MOT?
Yes. It takes less than a minute and can avoid an easy failure.
Do front number plate lights matter?
Number plate illumination applies to the rear registration plate.