Buick Invicta Back Up Light Bulb Size

The Buick Invicta back up light uses bulb size 1073 and bulb size P21W for the lighting system. Data for the lighting components covers the range from 1959 to 1963.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
1961-1963	P21W
1959-1960	1073

Bulb Specifications

Description	Bulb Size
ECE standard (Europe & worldwide). Single-filament signalling bulb with BA15s bayonet base. 12V, 21W.	P21W
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. Lower wattage variant of 1156. 12V, 13W.	1073

Other Locations

Additional Notes

The Buick Invicta back up light specifications cover model years 1959 through 1963, split across two distinct bulb types depending on the year.
The P21W bulb is specified for the 1961-1963 Buick Invicta. It follows the ECE standard, which governs lighting equipment across Europe and much of the world.
The 1073 bulb is specified for the 1959-1960 model years. It follows the ANSI standard, the North American system for automotive bulb classification.
Both the P21W and the 1073 are single-filament bulbs, meaning each serves one lighting function rather than combining two functions such as stop and tail in a single unit.
Both bulbs share the BA15s bayonet base type. This is a single-contact bayonet fitting with a 15mm base width, where the "s" denotes a single contact point at the base.
Both bulbs operate at 12 volts, consistent with the standard electrical system voltage of conventional passenger vehicles of that era.
The P21W operates at 21 watts, while the 1073 operates at 13 watts. The 1073 is described as a lower wattage variant of the 1156 bulb, which shares the same BA15s base but draws more current.
Although the P21W and 1073 share the same BA15s base type, their wattage ratings differ significantly. This electrical difference is a relevant fitment consideration when substituting one for the other.