GMC B7 front and rear side marker bulbs require 1157 size bulbs for proper illumination. The replacement chart covers 1996 to 2002 model years with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC B7 uses the 1157 bulb for both front and rear side markers across the 1996-2002 model years.
The 1157 is an ANSI-standardized bulb type recognized in the United States and Canada, making it a widely distributed incandescent format in North American automotive applications.
The 1157 is a dual-filament bulb, meaning it contains two separate filaments within a single glass envelope, each operating at a different wattage.
The bulb operates on a 12-volt electrical system and carries a 21W/5W rating, where the higher wattage filament serves the primary function and the lower wattage filament serves a secondary function such as a running or marker light.
The 1157 uses a BAY15d bayonet base, which is an offset double-contact base. The offset pin configuration is a deliberate design feature that prevents incorrect insertion into the socket.
Because the GMC B7 (1996-2002) uses the same 1157 bulb in both the front and rear side marker positions, the same bulb type is interchangeable between those two positions on the vehicle.
The BAY15d base of the 1157 is not physically compatible with single-contact bayonet bases such as the BA15s, which is used by bulbs like the 1156. Substituting a single-filament bulb in a dual-filament socket would result in incomplete circuit function.