Collection: Motorcycle & Scooter (12V / 6V) > Tail Lights, Brake Lights & Turn Signals

Motorcycle Signal Bulbs

Motorcycle signal lights serve three distinct functions:

• Turn Signals — mandatory orange/amber in color
• Brake Light — red, illuminates when braking
• Taillight — red, continuously lit with the headlights

On some motorcycles, the taillight and brake light are combined into a single dual-filament bulb (P21/5W).

P21W and BA15S: The Two Essential Bases

P21W (BA15S) — single-filament 21W bulb, 15mm bayonet base with symmetrical pins. Used for turn signals, reverse lights, and fog lights. The most common in motorcycle signaling.

BAY15D (P21/5W) — dual-filament bulb (21W + 5W), bayonet base with offset pins. Combines brake light (21W) and taillight (5W) in a single bulb. Found on motorcycles with a single taillight.

BAU15S (PY21W) — base with 30° offset pins, orange bulb for specific turn signals.

Switching to LED for Motorcycle Turn Signals

Switching to LED offers several advantages: 5 times faster response (useful for the brake light), 10× longer lifespan, reduced consumption.

Beware of hyperflashing: LEDs consume less power than an equivalent halogen bulb — the motorcycle's turn signal relay interprets this drop as a blown bulb and speeds up the flashing rate. Two solutions:

• Canbus LED with integrated resistor (simulates halogen consumption)
• External load resistor (50 W / 6 Ω) wired in parallel with each turn signal

Without this precaution, the turn signal will flash too quickly — non-compliant with road regulations and risking a failed inspection.

Finding Your Bulb Base

Remove your faulty bulb: the type is engraved on the base ("P21W BA15S 21W 12V"). Otherwise, consult your motorcycle manual, which lists the bulbs for each light.