Bulb Kit buying guide — what to know before you buy
A bulb kit groups the most common bulbs needed for a vehicle into a single box, covering exterior lighting (dipped beam, sidelight, indicator, brake, fog) and often a small selection of interior bulbs. Useful for MOT preparation, long journeys, and complying with legal requirements in some European countries to carry spares.
When to replace
Replace bulbs as soon as a failure is noticed. A blown headlight or brake light is an MOT failure and unsafe at night.
- Any exterior bulb has failed
- Bulbs visibly darkened — output reduced even though they still light
- MOT preparation — pre-emptively replace any dim bulbs
- Long European journey — many countries require a spare bulb kit
- Bulb age over five years on a daily-driven vehicle
What to look for when buying
Bulb kits must contain the correct format for your vehicle. The owner's manual lists the bulb codes for every position.
- Identify all bulb formats (H1, H4, H7, H11, HB3, HB4, W5W, W21W, P21W, etc.)
- Confirm the correct fuse ratings if the kit includes spare fuses
- LED replacements must be compatible with CANbus systems — most factory holders are designed for incandescent draw
- Long-life or +30/+90/+130 % output options for headlight bulbs
- Carry only the bulbs your vehicle actually uses — generic kits include redundant bulbs
Common failure modes
Bulb failure is mostly age and vibration related. Some failures point to a wider electrical fault.
- Filament failure from vibration or temperature cycling
- Reflector contamination if the bulb is touched with bare fingers
- Connector corrosion causing intermittent operation
- Repeated quick failure suggests over-voltage from a faulty regulator
- Moisture ingress into the headlight unit shortens bulb life
Related parts to check together
When fitting bulbs, take a moment to confirm related electrical parts are healthy.
- Headlight unit — check for cracks and condensation that shorten bulb life
- Indicator unit and lens — replace cracked lenses to prevent water ingress
- LED resistors — required for some LED indicator bulbs to avoid hyper-flash
- Fuse box — inspect for evidence of repeated bulb fuse failures