Pontiac Bonneville Back Up Light Bulb Size

Additional Notes

• The 1156 bulb is the most frequently specified back up light bulb across the Pontiac Bonneville's production history, appearing across the majority of model years from 1960 through 1999. It is a single-filament, 12V, 21W bulb with a BA15s bayonet base, conforming to ANSI standards for the US and Canadian markets.
• The 3057 is a dual-filament wedge bulb (T25) rated at 12V with a 27W high filament and 7W low filament. The Pontiac Bonneville (2000-2003) uses this bulb for the back up light, making it the most recent specification in the data.
• The 1141 shares the same BA15s bayonet base and 12V, 21W rating as the 1156, though the two are distinct ANSI part numbers. The Bonneville uses the 1141 in 1993 and 1995, while surrounding model years use the 1156, which means the bulbs are not confirmed as interchangeable despite their similar electrical ratings.
• The 2057 is a dual-filament bulb with a BAY15d bayonet base, rated at 12V with a 26.9W high filament and 8W low filament. It is specified for the Bonneville in 1988-1990 and is described as a brighter variant of the 1157.
• The 1157 is a dual-filament bulb with a BAY15d bayonet base, rated at 12V with a 21W high filament and 5W low filament. It is specified for the Bonneville in 1969-1970 and 1973. Although the 2057 and 1157 share the same BAY15d base type, their wattage ratings differ, and the specifications treat them as separate fitments.
• The 1073 is a single-filament bulb with a BA15s bayonet base, rated at 12V and 13W. It is specified for the Bonneville in 1957-1959 and 1963, and carries a lower wattage than the 1156 despite sharing the same base type. The lower wattage reflects the lower output requirements of earlier back up light applications.
• The BAY15d base used by the 2057 and 1157 has offset locating pins, which prevents it from being inserted into a BA15s socket. This physical difference means dual-filament bulbs specified for certain Bonneville model years are not socket-compatible with the single-filament BA15s bulbs used in other years.
• The 3057 uses a wedge-type base rather than a bayonet base, which is a fundamentally different mounting system from all other bulb types in these specifications. This makes the 2000-2003 Bonneville back up light housing mechanically incompatible with the bayonet-base bulbs used in earlier model years.
• Both the 1156 and 1073 use the BA15s bayonet base, but their wattage ratings differ at 21W and 13W respectively. Substituting one for the other in Bonneville applications where each is specified would result in a mismatch with the original electrical output intended for that model year.
• All bulb types in these specifications conform to ANSI standards applicable to the US and Canadian markets, indicating that the fitment data applies to North American market Bonneville vehicles across the full range of model years listed.