Chrysler St Regis Back Up Light Bulb Size

The Chrysler St Regis back up light requires bulb size 1073 or 1129 depending on the specific application. Data for the bulb sizes covers the range from 1955 to 1956.

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
1956	1073
1955	1129

Bulb Specifications

Description	Bulb Size
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 1073 bulb is an ANSI-standard single-filament bulb rated at 12V and 13W, fitted with a BA15s bayonet base. It is classified as a lower-wattage variant of the more common 1156 bulb.
The 1129 bulb is an ANSI-standard dual-filament bulb rated at 12V with a dual-wattage output of 21W and 5W, fitted with a BAY15d bayonet base. It is a variant of the 1157 bulb.
The BA15s base on the 1073 accepts a single contact pin, while the BAY15d base on the 1129 uses two offset contact pins to support its dual-filament configuration. These two base types are not interchangeable.
The 1956 Chrysler St Regis uses the 1073 bulb for the back up light, while the 1955 model uses the 1129 bulb. The difference in base type and filament count between these two bulbs means one cannot substitute for the other.
The shift from a dual-filament 1129 in 1955 to a single-filament 1073 in 1956 reflects a change in the back up light circuit design between those two model years.