The Difference Between Tail Lights and Brake Lights
Although they often share the same red lens housing at the rear of your car, tail lights and brake lights are separate circuits that serve different purposes.
| Light | When It's On | Purpose |
|---|---|---|
| Tail light | Whenever headlights or parking lights are on | Makes the rear of your car visible to traffic behind you at night or in low visibility |
| Brake light | When the brake pedal is pressed | Signals to following drivers that you are slowing or stopping |
| Reversing light | When reverse gear is selected | Illuminates the area behind the car; white coloured |
| Indicator (turn signal) | When indicator stalk is activated | Signals a turn or lane change; amber coloured |
Most NZ passenger cars also have a high-mounted brake light (third brake light) on the rear parcel shelf or above the boot. This is a legal requirement on cars manufactured after a certain date and is inspected at every WoF.
How They Work
On older vehicles, separate filament bulbs handle each function. Many modern cars use a dual-filament bulb where one filament provides the dimmer tail light and a second, brighter filament activates for braking. LED assemblies use separate LED arrays per function, controlled by the body control module.
Brake light activation is controlled by a brake light switch mounted on the brake pedal bracket. When the pedal is pressed, the switch closes the circuit, powering the brake lights. A faulty brake light switch means no brake lights even if all bulbs are fine.
What Causes Tail or Brake Lights to Fail?
- Blown bulb — most common. Filament bulbs fail with age; heat and vibration accelerate failure
- Blown fuse — a short circuit or overloaded circuit may blow the fuse protecting the tail light or brake light circuit
- Corroded bulb socket — moisture ingress causes the socket contacts to corrode; the bulb makes poor contact and may not light or may flicker
- Faulty brake light switch — all brake lights fail simultaneously
- Broken wiring — particularly common on hatchbacks and estates where the wiring flexes with the tailgate; repeated opening and closing fatigues the harness
- Water ingress into the light unit — cracked lens or perished seal allows water in, corroding the internals
- Faulty LED array — on modern cars with full LED assemblies, individual LEDs can fail. Partial failures (a section of LEDs out) are common
How to Check Your Lights
It is difficult to check your own brake lights without a helper. Options:
- Ask a passenger or bystander to stand behind the car while you press the brake
- Reverse slowly up to a reflective surface (garage door, shop window) and press the brake — look for the reflection
- Use a phone camera set to record and press the brake
Tail lights are easier — turn on the headlights and walk around the car.
Can You Replace Bulbs Yourself?
For older vehicles with conventional filament bulbs — often yes. Many tail and brake light bulbs are accessible via the boot or tailgate, behind a trim panel. The process:
- Remove the trim panel to access the back of the light unit (or remove the whole light unit from the outside)
- Twist the bulb holder and pull it out
- Replace the bulb (use the correct type — check the owner's manual or old bulb)
- Reinstall and test
On modern vehicles with LED assemblies or complex multi-function units, replacement may require workshop equipment or even replacement of the entire light unit.
WoF Implications
All rear lights are checked at every WoF. Failures include:
- Tail light not working
- One or more brake lights not working (the high-mounted brake light is also checked)
- Indicator not working
- Cracked lens that allows water ingress or changes the light colour
- Reversing light inoperative
A single blown bulb is an automatic WoF failure — it is one of the easiest and cheapest repairs to make before your inspection.
How Much Does Tail/Brake Light Repair Cost in NZ?
| Service | Estimated NZD Cost |
|---|---|
| Bulb replacement (per bulb, DIY) | $5–$25 (parts only) |
| Bulb replacement (workshop, parts + labour) | $30–$80 |
| Brake light switch replacement | $80–$180 |
| Tail light unit replacement (used) | $80–$250 |
| LED tail light unit replacement (new) | $200–$600+ |
When to Book a Mechanic
Fix failed lights before driving at night or before your WoF. A rear-end collision because the driver behind could not see you slow down is a severe consequence of ignoring a brake light fault. Many NZ Police stations and some mechanics offer a free basic light check — take advantage of this if you're unsure.