Subaru Forester Tail Light Bulb Size

Additional Notes

• The 7443 is the most widely specified tail light bulb across the Subaru Forester's history, covering model years 2001-2016. It is an ANSI-standard dual-filament wedge bulb in the T20 form factor, rated at 12V with a 21W/5W output split between its two filaments, where the higher wattage filament serves the brake or turn function and the lower wattage filament serves the running light function.
• The 1157 bulb was specified for the Subaru Forester in 1998-2000. Like the 7443, it is a dual-filament 12V bulb with a 21W/5W rating, but it uses a BAY15d bayonet base rather than a wedge-style base, making it physically incompatible with sockets designed for the 7443.
• The 12961 is a Philips-designated part number for a T10 miniature wedge bulb with a W2.1x9.5d base, rated at 12V and 5W. Its single-filament, low-wattage design contrasts sharply with the dual-filament 7443 it replaced in the Forester's tail light application from 2017 onward.
• The Subaru Forester (2017-2018 and 2023-2024) uses the 12961 bulb, which operates at 5W compared to the 21W brake filament of the 7443. This difference reflects a change in the tail light assembly's design rather than a reduction in light output, as later assemblies are engineered around lower-wattage light sources.
• The base types across the three specified bulbs are entirely distinct. The 1157 uses a BAY15d bayonet base, the 7443 uses a T20 wedge base, and the 12961 uses a W2.1x9.5d wedge base. None of these bulbs are interchangeable with one another, as each requires a differently shaped socket.
• The 7443 and 1157 share identical voltage and wattage ratings at 12V and 21W/5W, but their differing base configurations mean a 1157 cannot be substituted into a 7443 socket or vice versa, despite the electrical equivalence.
• The 12961 is a proprietary Philips part number rather than an ANSI industry standard, whereas both the 7443 and 1157 are defined under ANSI standards applicable in the United States and Canada.