Tail and brake light

The tail light is the red lamp at the back. On most bikes one bulb with two filaments does both jobs: a dim filament for the tail light and a bright one for the brake light. Newer bikes use LED units. A small white lamp lights the number plate.

What it does

The tail light shows your bike to drivers behind at night. The brake light comes on bright when either brake light switch closes. Filaments break from vibration; bulb holders rust from water; LED units fail when water gets in. A bulb fitted the wrong way round can light the wrong filament.

Signs it is worn or failing

• Tail light does not work.
• Brake light does not work.
• Brake light stays on: this can also flatten the battery.
• Cracked lens, water inside, rusty holder.

When to replace it

Replace the bulb when a filament is broken or the glass is black. Replace the lens if cracked, and the LED unit if any section is dark.

What to match when buying

• Match bulb type and wattage. Two-filament bulbs have offset pins so they fit only one way; do not force them.
• Look for an approval mark on the lamp. A red lens must stay red: do not fit a clear lens with a coloured bulb unless it is approved.
• Check the lens gasket is included.

Fitting notes

• Rider job: Replace a bulb. Check the lens seal when refitting, as the K-Light manual says.
• Test with someone pressing each brake: Test and adjust the brake light switches.
• If power is missing: Test a lighting circuit.

Reference (K-Light 125)