The Saab 99 front turn signal uses a P21/5W bulb size while the rear turn signal requires a P21W bulb size. The replacement chart covers 1975 to 1980 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 Saab 99 uses two distinct bulb types across its front and rear turn signal positions: the P21/5W for the front and the P21W for the rear, both governed by ECE standards recognized across Europe and worldwide.
Both bulb types operate on a 12-volt electrical system, which was the standard automotive voltage architecture during the production years covered by these specifications.
The P21/5W is a dual-filament bulb, meaning it carries two separate filaments within a single envelope, rated at 21 watts and 5 watts respectively. This dual-filament design allows one bulb to serve more than one lighting function simultaneously.
The P21W is a single-filament bulb rated at 21 watts, dedicated solely to its assigned signalling function without a secondary filament.
The Saab 99 front turn signal position across model years 1975-1980 exclusively uses the P21/5W, which is fitted with a BAY15d bayonet base. The BAY15d base features offset pins to prevent incorrect insertion, a design characteristic that distinguishes it from single-filament bases.
The rear turn signal position across the same 1975-1980 span uses the P21W, which is fitted with a BA15s bayonet base. The BA15s is a single-contact base with symmetrically placed pins.
Because the P21/5W uses a BAY15d base and the P21W uses a BA15s base, the two bulb types are not interchangeable. The physical base configurations differ in both pin alignment and contact count.
Despite sharing the same 21-watt primary filament output, the P21/5W and P21W serve structurally different roles and cannot substitute for one another due to their incompatible base designs.