The Fiat 131 front turn signal requires a 1157 bulb size while the rear turn signal uses a 1156 bulb size. The replacement chart covers 1975 to 1978 model 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 Fiat 131 uses the 1157 bulb for the front turn signal across the 1975-1978 model years.
The 1157 is a dual-filament bulb operating at 12V with a 21W/5W output, meaning the two filaments serve different functions, typically combining a brighter turn signal with a dimmer running or parking light in a single housing.
The 1157 uses a BAY15d bayonet base, which features two offset pins to prevent incorrect installation of a single-filament bulb in its place.
The rear turn signal on the Fiat 131 uses the 1156 bulb across the same 1975-1978 model years.
The 1156 is a single-filament bulb rated at 12V and 21W, with a BA15s bayonet base that has two pins positioned symmetrically.
Although the 1157 and 1156 share a similar physical profile and both use bayonet-style bases, their pin configurations differ. The BAY15d base of the 1157 is not interchangeable with the BA15s base of the 1156.
Both the 1157 and 1156 are ANSI-standardized bulbs recognized in the United States and Canada, indicating consistent availability across the North American market during the production period of the Fiat 131.
The separation of bulb types between front and rear positions on the Fiat 131 reflects a functional distinction, where the front position requires dual-filament capability and the rear requires only a single filament for the turn signal function.