Guides | PlentyTorque UK

A blown headlight bulb is both an MOT failure and a safety risk, so it's worth knowing how to swap one yourself. In many cars it's a ten-minute job; in others the whole assembly may need to come out. This guide covers bulb types, fitting and getting your beam alignment right afterwards.

Identify your bulb type

The first job is knowing exactly what you need. Common UK headlight bulb fittings include:

• H7 and H4 — the most widespread halogen fittings. H4 is dual-filament (dip and main in one bulb); H7 is single-filament.
• H1, H11, HB3, HB4 — found across many makes for dip, main or fog use.
• HID/Xenon — brighter gas-discharge bulbs (D1S, D2S etc) found on higher-spec cars; handle with care as they run at high voltage.
• LED units — often sealed assemblies where the whole unit is replaced rather than a single bulb.

Check your handbook or the old bulb's markings, and browse the right fitting in our automotive light bulbs range. If a full unit is cracked or fogged, see our headlight assemblies. Don't forget your fog lights if they need attention too.

What you'll need

• The correct replacement bulb or assembly
• Clean gloves or a tissue (never touch halogen glass with bare fingers)
• A small screwdriver or trim tools
• A torch and possibly a socket set for assembly removal

Replacing a bulb

• Switch off the lights and ignition, and open the bonnet.
• Access the back of the headlight. You'll usually find a rubber dust cover or a screw-off cap. On tight engine bays you may need to remove the air filter box or washer bottle for access.
• Disconnect the wiring connector and release the retaining clip or twist-lock holding the bulb.
• Remove the old bulb and fit the new one without touching the glass — skin oils create hot spots that shorten bulb life. Use a tissue or gloves.
• Reconnect the clip, wiring and dust cover, then test before closing the bonnet.

It's good practice to replace bulbs in pairs. They dim with age, so a matched pair keeps your light output even and avoids a second job a few weeks later.

Replacing a full assembly

If the lens is cracked, yellowed or the unit is water-damaged, you'll replace the whole assembly. Typically you'll remove a section of trim or the bumper edge, undo two or three bolts, unplug the connectors and lift the unit out. Fit the new assembly in reverse, making sure all clips and bolts are secure so it can't move on the road.

Beam alignment — don't skip it

After fitting a new bulb or assembly, your headlight aim may be slightly off. Badly aligned headlights dazzle oncoming drivers and will fail the MOT. Most headlights have adjuster screws on the top or side of the unit. For a rough home check:

• Park 5 metres from a flat wall on level ground.
• Mark the centre of each beam.
• The dipped beam should sit slightly below the centre marks and not point upward.

For a precise, MOT-standard setup, a garage with proper beam-setting equipment is the reliable option — it only takes a few minutes.

Older and discontinued units

Finding a headlight assembly for an older or rarer model can be tricky. Search using your registration or the OE part number stamped on the old unit. If you can't find it listed, use our request-a-part service and we'll help track down the correct fitment, including classic and discontinued lights.

Frequently asked questions

Why shouldn't I touch a halogen bulb glass?

Oils from your skin create hot spots on the glass that can cause the bulb to fail prematurely or even shatter. Hold the bulb by its metal base, or use gloves or a clean tissue when fitting.

Should I replace headlight bulbs in pairs?

Yes, it's recommended. Bulbs dim gradually, so fitting a matched pair keeps left and right output even and avoids the other side blowing soon after, which would mean repeating the job.

Will new headlights need realigning?

Often, yes. After fitting a bulb or assembly the beam aim can shift. Misaligned headlights dazzle others and fail the MOT, so check the alignment and have a garage set it precisely if unsure.