Saturn L100 front turn signal bulbs use 3457 size while rear turn signal bulbs use P21W size. The replacement chart covers 2001 to 2002 vehicle production years with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Saturn L100 uses two distinct bulb standards across its front and rear turn signal positions, with the front drawing from the ANSI system used in the United States and Canada, and the rear drawing from the ECE system common in Europe and worldwide markets.
The 3457 bulb, fitted to the front turn signal positions of the Saturn L100 for 2001-2002, is a dual-filament T25 wedge bulb rated at 12V with a 27W primary filament and a 7W secondary filament.
The dual-filament design of the 3457 allows a single bulb to serve two lighting functions simultaneously, with the higher-wattage filament typically handling the turn signal flash and the lower-wattage filament serving a secondary role such as a parking or running light.
The P21W bulb, fitted to the rear turn signal positions for 2001-2002, is a single-filament signalling bulb rated at 12V and 21W, meaning it performs only one lighting function at that position.
The P21W uses a BA15s bayonet base, which is a single-contact bayonet mount. This base type is not interchangeable with the wedge base of the 3457, making front and rear bulbs incompatible with each other despite sharing the same 12V operating voltage.
The T25 wedge base of the 3457 and the BA15s bayonet base of the P21W represent physically different mounting systems, so substituting one for the other at any position on the Saturn L100 is not possible without modification to the socket.
Although both bulbs operate at 12V, their wattage ratings differ. The 3457 carries a 27W primary filament while the P21W is rated at 21W, reflecting a difference in light output between the front and rear turn signal positions.