Triumph TR7 Brake Bulb Size

The Triumph TR7 brake light requires a 1157 bulb size for proper illumination and function within the rear lighting assembly. Data for the specified component covers the range from 1975 through 1981.

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
1975-1981	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 Triumph TR7 uses the 1157 bulb across all listed model years, spanning 1975-1981.
The 1157 is an ANSI-standardized bulb type, meaning its physical and electrical specifications are governed by a recognized North American standard used in both the United States and Canada.
The 1157 is a dual-filament bulb, which allows it to serve two lighting functions within a single unit. In brake light applications, the higher-wattage filament activates under braking while the lower-wattage filament handles a secondary function such as running or tail light operation.
The bulb operates at 12 volts with a wattage rating of 21W for the primary filament and 5W for the secondary filament.
The 1157 uses a BAY15d bayonet base. The BAY15d designation indicates an offset dual-contact base, where the two pins are positioned at different heights to prevent incorrect insertion of a single-filament bulb into a dual-filament socket.
Because the BAY15d base is offset, a single-filament 1156 bulb, which shares a similar bayonet form but uses a BAY15s base with pins at equal heights, is not a direct substitute for the 1157 in the Triumph TR7.