The Mazda Cosmo front and rear turn signal bulbs both utilize a 1157 bulb size. The replacement chart covers 1976 to 1978 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 1157 is the sole bulb type listed across all turn signal positions in the Mazda Cosmo specifications covered, appearing in both front and rear applications for the 1976-1978 model years.
The 1157 is a dual-filament bulb, meaning it houses two separate filaments within a single envelope. The higher-output filament operates at 21W and serves the active turn signal function, while the 5W filament handles a lower-intensity steady-state role.
The 1157 operates on a 12V electrical system, which is standard for automotive applications of this era.
The base type on the 1157 is a BAY15d bayonet mount. This base features two offset pins at different heights, a design that prevents incorrect insertion by ensuring the bulb can only be seated in one orientation.
The 1157 carries ANSI standardization and is recognized across both the United States and Canadian markets, reflecting a widely distributed specification rather than a region-specific one.
The front and rear turn signal positions on the Mazda Cosmo (1976-1978) share an identical bulb specification, meaning the same 1157 unit fits both locations without substitution or adaptation.
The BAY15d base of the 1157 is not interchangeable with single-filament bayonet bases such as the BA15s, which lacks the offset pin configuration required for dual-filament alignment.