Ford Mainline Back Up Light Bulb Size

The Ford Mainline back up light requires bulb size 1141 or 1129 depending on the specific application for the vehicle. Data for the bulb sizes covers the range from 1953 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	1141
1953-1955	1129

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1141
ANSI standard (US & Canada). Dual-filament bulb with BAY15d bayonet base. Variant of 1157. 12V, 21/5W.	1129

Other Locations

Additional Notes

The Ford Mainline backup light specifications cover model years 1953 through 1956, with two distinct bulb types used across that production span.
The 1141 bulb is a single-filament type rated at 12V and 21W, fitted with a BA15s bayonet base, and conforms to ANSI standards recognized in both the United States and Canada.
The 1129 bulb is a dual-filament type rated at 12V with a 21/5W output split between its two filaments, fitted with a BAY15d bayonet base, and also carries ANSI recognition in the United States and Canada.
The BA15s base of the 1141 and the BAY15d base of the 1129 are not interchangeable. The BAY15d base uses offset locating pins to prevent incorrect installation, while the BA15s base uses a single-pin alignment, making the two physically incompatible.
The Ford Mainline (1956) takes the 1141 bulb, which is a single-filament design, distinguishing it from the earlier model years in this specification set.
The 1129 bulb applies to the Ford Mainline for model years 1953-1955, representing three consecutive years on the same bulb specification.
The 1129 is noted as a variant of the 1157 bulb. Despite that relationship, the two are not direct substitutes, as wattage ratings and base pin configurations can differ between variants.
The dual-filament nature of the 1129 means it carries two separate wattage ratings: 21W for the primary filament and 5W for the secondary filament, a characteristic absent in the single-filament 1141.