The Mitsubishi Sigma brake light requires a 1157 bulb size for the specific lighting component located at the rear of the vehicle. Data for the bulb specifications covers the range from 1989 to 1990.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mitsubishi Sigma uses the 1157 bulb for the brake light position across both 1989-1990 model years.
The 1157 is a dual-filament bulb with a BAY15d bayonet base, rated at 12V and 21W/5W. The dual-filament design allows it to serve both a high-intensity brake function and a lower-intensity running light function within a single unit.
The BAY15d bayonet base features offset pins, which physically prevent incorrect installation of a single-filament bulb in a socket requiring dual-filament operation.
The center high mount stop light (CHMSL) on the Sigma does not share a bulb type with the standard brake light position, and the two positions are not interchangeable.
The CHMSL bulb specification changed between model years: the 1989 Sigma uses a 921, while the 1990 model uses a 168.
The 921 is a T15 wedge bulb rated at 12V and 16W, while the 168 is a smaller T10 wedge bulb rated at 12V and 4.9W. The wattage difference between these two types is substantial, and substituting one for the other would result in either under- or over-illumination of the CHMSL.
T10 and T15 designations refer to the outer envelope width of the bulb in eighths of an inch, meaning the T15 is physically wider than the T10. This size difference affects socket fitment, and the two wedge types are not mechanically interchangeable.
All three bulb types listed, the 1157, 168, and 921, conform to ANSI standards applicable in both the United States and Canada.