How do I replace a brake light globe?

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Quick answer

Get someone to press the brake pedal so you can see which light is out, then open the rear lamp access panel in the boot (or remove the tail light unit, as your owner’s manual describes), twist out the globe holder and swap the globe for one of the same type, often a P21/5W or P21W bayonet or a wedge-type globe. If both brake lights and the high third brake light are out together, the problem is more likely the fuse or brake light switch than the globes.

Is this a DIY job?

  • Difficulty: Easy
  • Time: 10 to 30 minutes
  • Tools: owner’s manual, screwdriver or trim tool (some cars), clean cloth
  • Skills: none beyond care with plastic clips

On most cars this is a simple job from inside the boot or tailgate. Some cars need the tail light unit unbolted and pulled out, which is still a DIY job if you’re patient with the clips.

Step by step

Common bayonet globe bases: BA15s, BAY15d and BAU15s Three 15 mm bayonet globes. BA15s (for example P21W): two locating pins opposite each other at the same height and one contact on the bottom. BAY15d (for example P21/5W): pins at different heights and two contacts on the bottom, so it only fits one way. BAU15s (for example amber PY21W): pins at the same height but not opposite each other, and one contact. Bayonet globe bases: how to tell them apart Side view (top row) and looking at the bottom of the base (bottom row). Not to scale. BA15s Pins level, opposite BAY15d Pins at different heights BAU15s Pins level, not opposite One contact Two contacts One contact, offset pin e.g. P21W (brake, reverse) e.g. P21/5W (brake + tail) e.g. PY21W (amber indicator) Always confirm the globe code in your owner’s manual or on the old globe before buying.
Common bayonet globe bases: BA15s, BAY15d and BAU15s
  1. Find out which light is out. Have a helper press the brake pedal while you look at both brake lights and the high-mounted third brake light. No helper? Reverse up close to a garage door or shop window at night and use your mirrors.
  2. Check the pattern. If only one brake light is out, it’s almost certainly the globe. If all brake lights are out, check the fuse and the brake light switch at the pedal before buying globes.
  3. Find the globe type. The owner’s manual lists it. Common types are P21/5W (brake and tail in one globe), P21W (brake only) and W21/5W (wedge type, brake and tail). Buy a pair.
  4. Switch everything off. Ignition off, lights off.
  5. Get to the back of the lamp. Open the boot and look for a small access cover or panel behind the tail light. Some cars instead need two or three nuts or screws undone so the whole tail light unit can be eased out. Protect the paint with a cloth.
  6. Remove the globe holder. Most holders twist anticlockwise about a quarter turn and pull out. Some are a carrier plate with several globes, released by plastic tabs.
  7. Remove the old globe. Bayonet globes: push in gently, twist anticlockwise and pull out. Wedge globes: pull straight out.
  8. Check the old globe and holder. A blackened glass or broken filament confirms the globe has failed. Look for corrosion or melted plastic in the holder. Green corrosion can be cleaned off with a small brush and contact cleaner.
  9. Fit the new globe. A P21/5W globe has offset pins so it only fits one way. Don’t force it: if it won’t go in, turn it 180 degrees. Getting it in the wrong way round isn’t possible with a correct globe, but forcing it can damage the holder.
  10. Refit the holder and test. Check the brake light, tail light and indicator on that side before you refit any covers. Then refit the unit or cover and make sure any seals sit properly so water stays out.

Specs table

Common rear lamp globe types (12V)

Type Filaments Wattage Base Typical use Notes
P21/5W 2 21/5 W BAY15d (offset pins, two contacts) Brake and tail in one globe Often sold as “1157-type”
P21W 1 21 W BA15s (level pins, one contact) Brake only, reverse, rear fog Often sold as “1156-type”
W21/5W 2 21/5 W W3x16q (wedge) Brake and tail in one globe US equivalent 7443
W21W 1 21 W W3x16d (wedge) Brake only, reverse US equivalent 7440

US 1156 and 1157 globes fit the same bases as P21W and P21/5W but aren’t identical in rating. Buy by the code in your owner’s manual where you can.

What you’ll need

  • P21/5W globe or P21W globe or W21/5W wedge globe (whichever your manual specifies)
  • electrical contact cleaner (if the holder is corroded)
  • Spare blade fuses (if all brake lights are out)

When to call an auto electrician

  • All the brake lights are out and the fuse is fine. The brake light switch or wiring is the likely cause, and on many cars the switch also feeds cruise control, stop-start and the engine computer.
  • The brake lights stay on all the time. That can flatten the battery and confuses drivers behind you.
  • The high-mounted third brake light has failed. On many cars it’s a sealed LED unit that’s replaced as a whole.
  • The car’s tail lights are LED units. Most can’t be repaired by changing a globe.
  • A “lamp failure” warning stays on after the change, or the new globe works dimly or flickers.
  • The holder is melted or the wiring is burnt.

Need an auto electrician? Find local auto electricians and mobile services in your city.

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Related questions

Q: Is it illegal to drive with a brake light out? A: Brake lights are a required safety item. In Queensland, for example, a vehicle with a part that doesn’t work as intended counts as defective, and driving it can lead to a defect notice or fine. Check your own state’s rules. More importantly, the driver behind may not see you slow down. Replace it straight away.

Q: Why do both my brake light and tail light share a globe? A: A P21/5W or W21/5W globe has two filaments: a dim one for the tail light and a bright one for braking. One globe does both jobs.

Q: My new globe glows when I turn the headlights on and the indicator flashes oddly. Why? A: This often means a poor earth in the lamp unit or holder. Clean the earth connection and check the holder for corrosion.

Q: Can I fit LED globes in my brake lights? A: Some LED replacements are available, but they can cause lamp-failure warnings on CAN-bus vehicles, and their light pattern in a reflector designed for a filament globe may not be as bright. The lamp must still meet the Australian Design Rules.

Sources

  1. Wikipedia, “List of automotive light bulb types” – P21W, P21/5W, W21W and W21/5W bases, wattages and ANSI equivalents (7440, 7443). https://en.wikipedia.org/wiki/List_of_automotive_light_bulb_types (checked October 2026)
  2. Narva, “12V 21W P21W BA15S incandescent globe” (part 47382) – P21W is 12V 21W on a BA15s base. https://www.narva.com.au/products/47382 (checked October 2026)
  3. Narva, “12V 21/5W BAY15d globe” (part 17916BL) – 21/5W dual-filament on a BAY15d offset-pin base for stop/tail. https://www.narva.com.au/products/17916BL (checked October 2026)
  4. Queensland Government, Transport Operations (Road Use Management—Vehicle Standards and Safety) Regulation 2021, ss 7–9 – a vehicle is defective if a component doesn’t perform its intended function; offence to drive a defective vehicle; defect notices. https://www.legislation.qld.gov.au/view/whole/html/inforce/2026-07-01/sl-2021-0114 (checked October 2026)

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