Ford Thunderbird Back Up Light Bulb Size

Additional Notes

• The 1156 bulb is the most frequently specified backup light size across the Ford Thunderbird's model history, covering the 1959-1961 and 1968-1988 model years.
• The 1156 is a single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base, which is a single-contact base with a 15mm collar.
• The 2356 bulb appears across multiple non-consecutive model years and features a dual-filament design with a BAY15d bayonet base, which is a double-contact offset base that prevents incorrect installation.
• The 1076 and 1141 bulbs share the same BA15s bayonet base as the 1156, meaning the base type is physically compatible across these three bulb sizes, though wattage ratings differ.
• Despite sharing a base with the 1156 and 1141, the 1076 is rated at only 8W compared to the 21W of those two bulbs, making it a lower-output variant not interchangeable by wattage.
• The Ford Thunderbird (1955) uses the 1129 bulb, a dual-filament type with a BAY15d bayonet base rated at 21/5W, which is a variant of the 1157 family.
• The 3156 is a single-filament wedge bulb using a T25 wedge base rather than a bayonet base, distinguishing it physically from the 1156 and 1141 despite a similar 27W output range.
• The 2456 is a festoon-type bulb, which uses a cylindrical form factor held in place by end caps rather than a bayonet or wedge base, representing a distinct mounting style among the bulbs specified.
• The 1963-1967 model years share the 1076 specification, while the surrounding years use the higher-wattage 1156, indicating a period where a lower-output bulb was fitted to the backup light position.
• The 2356 and 1129 are the only dual-filament bulbs specified across the Thunderbird's backup light history, though a backup light application typically activates only one filament.