GMC C7000 front and rear turn signal bulbs utilize 1157, 1073, and 2057 sizes for front applications and 1157 and 1073 sizes for rear positions. The replacement chart covers 1979 through 1990 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.
The 1157 bulb is the most widely used turn signal bulb across the GMC C7000 specifications, serving both front and rear positions from 1979 through 1990 on standard and Medium Duty configurations.
The 1157 is a dual-filament bulb rated at 12V with a 21W bright filament and a 5W dim filament, mounted on a BAY15d bayonet base. The dual-filament design allows a single bulb to serve both turn signal and running light functions.
The 1073 bulb is specified exclusively for the Tiltmaster configuration of the GMC C7000, covering both front and rear turn signal positions from 1985 through 1990.
The 1073 is a single-filament bulb rated at 12V and 13W, using a BA15s bayonet base. Because it has only one filament, it serves a single lighting function rather than a combined one.
The BA15s base of the 1073 and the BAY15d base of the 1157 are physically distinct. The BAY15d base has two offset pins to enforce correct filament orientation, while the BA15s base has two aligned pins. These two bulbs are not interchangeable despite sharing a similar bayonet form factor.
The 2057 bulb is specified only for the 1984 Medium Duty front turn signal position. It shares the BAY15d bayonet base with the 1157 but operates at higher wattages, rated at 26.9W for the bright filament and 8W for the dim filament.
Although the 2057 and 1157 share the same BAY15d base, the 2057 draws more power. Substituting one for the other without confirming socket and circuit compatibility may affect performance or component load.
The 1984 Medium Duty configuration is notable in that the front turn signal uses a 2057 while the rear turn signal uses a 1157, meaning the front and rear positions in that year and configuration do not share the same bulb.
All three bulb types, the 1157, 1073, and 2057, conform to ANSI standards applicable in both the United States and Canada, indicating standardized electrical and physical tolerances across the specifications.
From 1979 through 1983, the specifications list only a single bulb size per position with no configuration sub-variants noted, whereas 1985 through 1990 consistently distinguish between Medium Duty and Tiltmaster configurations for both front and rear positions.