GMC 370 Dome Light Bulb Size

The GMC 370 dome light bulb uses a 1156 or 94 size bulb for this vehicle model. The replacement chart covers 1956 to 1959 production years with corresponding bulb size specifications.

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
1958-1959	1156
1956-1957	94

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156
ANSI standard (US & Canada). Dual-filament bulb with BAY15d bayonet base. Variant of 1157. 12V, 21/5W.	94

Other Locations

Additional Notes

The GMC 370 dome light uses two distinct bulb types across its production years: the 1156 for 1958-1959 and the 94 for 1956-1957.
Both the 1156 and 94 bulbs are ANSI-standardized components recognized in the United States and Canada, operating on a 12-volt electrical system.
The 1156 is a single-filament bulb rated at 21W, fitted with a BA15s bayonet base, which is a single-contact base with one locating pin.
The 94 is a dual-filament bulb rated at 21/5W, fitted with a BAY15d bayonet base, which is a double-contact base with two offset locating pins.
The BAY15d base of the 94 bulb is physically distinct from the BA15s base of the 1156, making the two bulbs non-interchangeable despite their similar bayonet-style mounting.
The 94 bulb is a variant of the 1157, sharing its dual-filament design and BAY15d base type, though the two are not necessarily identical in all electrical ratings.
The offset pins on the BAY15d base of the 94 bulb serve as a keying mechanism, ensuring the bulb is seated in a fixed rotational orientation within its socket.
The dual-filament construction of the 94 bulb provides two separate wattage outputs, 21W and 5W, each controlled independently through the two contact points at its base.