Plymouth Plaza Back Up Light Bulb Size

The Plymouth Plaza back up light requires bulb size 1129, 1073, or P21W depending on the specific application. Data for the bulb sizes covers the range from 1954 to 1958.

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
1958	P21W
1956-1957	1073
1954-1955	1129

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
ANSI standard (US & Canada). Dual-filament bulb with BAY15d bayonet base. Variant of 1157. 12V, 21/5W.	1129

Other Locations

Additional Notes

The Plymouth Plaza backup light specifications span model years 1954 through 1958, covering three distinct bulb types across that five-year period.
The 1073 bulb follows the ANSI standard used in the US and Canada. It is a single-filament bulb rated at 12V and 13W, fitted with a BA15s bayonet base, and it appears in the Plymouth Plaza for model years 1956-1957.
The 1073 is a lower-wattage variant of the more common 1156 bulb. At 13W, it produces less output than the 1156, which means substituting a 1156 in its place would result in higher wattage than the original specification calls for.
The 1129 bulb also follows the ANSI standard. It is a dual-filament bulb rated at 12V with a 21/5W output split, and it uses a BAY15d bayonet base. This bulb is specified for the Plymouth Plaza in model years 1954-1955.
The BAY15d base of the 1129 is physically distinct from the BA15s base of the 1073. The BAY15d base has offset pins to accommodate the dual-filament design, making the two bulbs mechanically incompatible with each other's sockets.
The 1129 is a variant of the 1157 bulb. The dual-filament construction of the 1129 is notable for a backup light application, as backup lights typically require only a single active filament.
The 1958 Plymouth Plaza uses the P21W bulb, which follows the ECE standard adopted in Europe and worldwide markets. It is a single-filament bulb rated at 12V and 21W, also fitted with a BA15s bayonet base.
Both the P21W and the 1073 share the BA15s bayonet base, but their wattage ratings differ significantly. The P21W operates at 21W while the 1073 operates at 13W, so the two are not interchangeable despite the shared base type.
The shift from the dual-filament 1129 in 1954-1955 to the single-filament 1073 in 1956-1957 represents a change in both base type and filament configuration across those model years.
The transition to the P21W in 1958 marks the only use of an ECE-standard bulb across the five model years covered in the specifications for the Plymouth Plaza backup light position.