Collection: P21W / P27W bulbs

The P21W Bulb: Role and Use

The P21W is a 21-watt bulb with a BA15S base (single pin). It is used for rear signaling:

• Turn signals (orange/amber)
• Reversing lights (white)
• Brake lights on some vehicles
• Rear fog lights on some models (red)

Its cylindrical shape and 21W power make it the standard for rear signaling on the vast majority of vehicles prior to 2005.

P21W or P21/5W: They Are Not the Same Bulb

A frequent confusion to clarify:

• P21W — 1 filament (21W), BA15S base with 1 centered pin. Single light intensity — single function.
• P21/5W — 2 filaments (21W + 5W), BAY15D base with 2 asymmetrical pins. Combines brake (21W) and side light (5W).

Visually similar, they are NOT interchangeable: the BAY15D base has its 2 pins at different heights to prevent inverted installation.

P21W LED for Turn Signals: Hyperflashing

An LED consumes less than a 21W halogen bulb — the on-board computer interprets this low consumption as a blown bulb and speeds up the flashing (hyperflashing).

Two solutions:

• Integrated P21W canbus LED bulb — resistance incorporated in the base, no additional components needed. Plug & play.
• External load resistor (50W/6Ω) — wired in parallel. More economical but more technical to install.

For reversing lights (white P21W), hyperflashing does not apply — the LED can be installed directly without special precautions.

The P27W

BA15S base similar to the P21W but at 27W — present on some recent vehicles for turn signals or reversing lights. P27W canbus LEDs offer the same advantages as P21W LEDs.