Triumph Spitfire Brake Bulb Size

The Triumph Spitfire brake light requires a bulb with the specific 1157 size for proper operation and visibility. Available data for the vehicle covers the period from 1973 through 1980.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
1973-1980	1157

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Dual-filament bulb with BAY15d bayonet base. 12V, 21W/5W.	1157

Other Locations

Additional Notes

The 1157 is the sole brake bulb type listed across all Triumph Spitfire model years in these specifications, covering the 1973-1980 range.
The 1157 is an ANSI-standardized bulb, meaning it conforms to a defined North American specification used in the United States and Canada.
As a dual-filament bulb, the 1157 contains two separate filaments within a single envelope, one rated at 21W for the brake function and one at 5W for a lower-intensity running light function.
The 1157 uses a BAY15d bayonet base, a two-pin offset base design that physically prevents incorrect insertion by positioning the two pins at different heights along the base.
The 1157 operates on a 12V electrical system, which aligns with the standard automotive voltage used in the Spitfire across this production period.
The BAY15d base of the 1157 is not interchangeable with single-filament bayonet bases such as the BA15s, as the pin configuration and internal wiring requirements differ between the two types.