Collection: Bulbs BAU15S

PY21W and BAU15S: the orange turn signal bulb

The PY21W (also noted BAU15S for its base) is a 21W bulb with an orange/amber tinted glass, used exclusively for turn signals. The orange color is mandated by traffic laws for turn signals—it is not legal to replace it with a white or different colored bulb for exterior use.

The BAU15S base has a 5° offset pin (the "U" in BAU15S) which physically prevents the installation of a white BA15S bulb in a housing designed for an orange bulb.

Difference between BAU15S and BA15S

• BA15S — single-contact bayonet base, straight pin. Used for P21W (white) — turn signals on some vehicles, reverse lights, single stop lights.
• BAU15S — single-contact bayonet base with a 5° angular offset. Specifically for PY21W (orange glass).

If your turn signal bulb is a PY21W, the housing only accepts a BAU15S base.

Orange LED PY21W: hyperflashing and canbus solution

Switching to LED PY21W provides a faster response and longer lifespan—but raises the issue of hyperflashing:

• An LED consumes less than a 21W halogen—the onboard computer detects low consumption and speeds up the flashing (abnormal rate).
• Solution 1: Canbus LED PY21W with integrated load resistor—the computer detects the correct consumption, normal flashing.
• Solution 2: External load resistor 50W/6Ω connected in parallel—economical but more technical installation.

Caution: the LED must remain orange/amber—a white LED for an exterior turn signal is illegal and may result in failure at the technical inspection.