BMW 2500 front turn signal bulbs use 1157 size while rear turn signal bulbs use 1156 size. The replacement chart covers 1969 to 1971 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 BMW 2500 uses the 1157 bulb for the front turn signal across the 1969-1971 model years.
The 1157 is a dual-filament bulb rated at 12V with a 21W/5W output, meaning it carries one filament for the turn signal function and a second, lower-wattage filament for a parking or running light function.
The 1157 uses a BAY15d bayonet base, which features two offset pins at different heights to prevent incorrect installation of a single-filament bulb in a dual-filament socket.
The rear turn signal on the BMW 2500 uses the 1156 bulb across the same 1969-1971 model years.
The 1156 is a single-filament bulb rated at 12V and 21W, dedicated solely to the turn signal function without a secondary filament.
The 1156 uses a BA15s bayonet base, which has two pins at equal heights, distinguishing it physically from the BAY15d base of the 1157.
Both the 1157 and 1156 are ANSI-standardized bulbs recognized in the United States and Canada, meaning they conform to a defined set of electrical and physical specifications.
The front and rear turn signal sockets on the BMW 2500 are not interchangeable, as the front requires a dual-filament 1157 with a BAY15d base while the rear requires a single-filament 1156 with a BA15s base.
Installing a 1156 in place of a 1157 would result in the loss of the secondary filament function, as the single-filament bulb cannot replicate the dual-filament behavior of the 1157.