The Opel 1900 front and rear turn signal bulbs utilize a 1157 or 1034 size. The replacement chart covers 1971 through 1975 production years with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Opel 1900 uses two distinct turn signal bulb types across its 1971-1975 model years: the 1034 for 1971-1972 and the 1157 for 1973-1975, applied identically to both front and rear positions in each respective year.
Both the 1034 and 1157 are ANSI-standardized bulbs recognized in the US and Canadian markets, meaning they conform to defined performance and dimensional standards rather than proprietary specifications.
The 1157 is a dual-filament bulb operating at 12 volts with a 21W high filament and a 5W low filament, allowing it to serve both turn signal and parking light functions from a single unit.
The 1034 shares the same dual-filament 12V, 21W/5W configuration as the 1157 and is classified as a variant of it, indicating a close functional relationship between the two types.
Both bulb types use the BAY15d bayonet base, a two-pin offset base design that physically prevents incorrect single-filament bulbs from being seated in the socket.
Because the 1034 is a variant of the 1157 and both share the BAY15d base and identical wattage ratings, physical fitment between the two types may be possible, though the specifications list them as distinct part numbers for specific model years.
The transition from the 1034 to the 1157 occurred between the 1972 and 1973 model years, affecting all four turn signal positions simultaneously.