The White/GMC J8C0 uses a 1157 bulb size for both front and rear turn signal applications. This replacement chart covers vehicle production spanning 1988 to 1989.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 1157 is the sole bulb type specified for the White/GMC J8C0 across all listed turn signal positions and model years.
The 1157 is a dual-filament bulb, meaning it contains two separate filaments within a single envelope, allowing it to serve two distinct lighting functions at different wattages.
It operates on a 12-volt electrical system and draws 21 watts on its primary filament and 5 watts on its secondary filament.
The 1157 uses a BAY15d bayonet base, which is an offset twin-pin mount. The two pins are positioned at different heights to ensure the bulb is inserted in the correct orientation, preventing filament misalignment.
The 1157 conforms to ANSI standards and is recognized in both the United States and Canada, reflecting a standardized specification shared across North American markets.
Both the front and rear turn signal positions on the J8C0 for the 1988-1989 model years share the same 1157 specification, indicating a uniform bulb requirement across all four turn signal sockets on the vehicle.
Because the BAY15d base uses offset pins, a bulb with a standard twin-pin bayonet base (BY15d) is not a compatible substitute, as the pin heights differ and the bases are not interchangeable.