The Triumph Spitfire front and rear turn signal bulbs utilize either 1157 or 1156 size bulbs depending on production specifications. The replacement chart covers 1973 to 1980 model years with corresponding bulb size data.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The two bulb types specified across all Triumph Spitfire turn signal positions are the 1156 and 1157, both of which are ANSI-standardized bulbs used in the United States and Canada markets.
The 1156 is a single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base. Its single filament means it serves one lighting function only, making it suitable for dedicated turn signal circuits.
The 1157 is a dual-filament bulb rated at 12V with a 21W/5W output, fitted with a BAY15d bayonet base. The two filaments allow it to serve two separate lighting functions, such as turn signaling and running light duties, within a single housing.
The BA15s base of the 1156 and the BAY15d base of the 1157 are not interchangeable. The BAY15d base features offset locating pins to prevent incorrect installation, while the BA15s base has symmetrically placed pins.
The Triumph Spitfire front turn signal position used the 1156 from 1973-1975 and transitioned to the 1157 from 1976-1980, reflecting a shift from a single-filament to a dual-filament application at that position.
The rear turn signal position used the 1156 from 1973-1979 across all listed years except 1980, when the specification changes to the 1157.
In the 1980 model year, both the front and rear turn signal positions share the same 1157 specification, whereas in all prior listed years at least one position called for the 1156.
Because the 1156 and 1157 differ in both filament count and base configuration, substituting one for the other is not supported by the specifications for any listed model year or position.