The White/GMC ACM uses 1157 bulb size for both front and rear turn signal applications. Replacement chart data spans 1988 to 1992 model 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 White/GMC ACM uses the 1157 bulb for both front and rear turn signals across the 1988-1992 model years.
The 1157 is a dual-filament bulb, meaning it carries two separate filaments within a single envelope, allowing it to serve more than one lighting function simultaneously.
It operates on a 12-volt electrical system and draws 21 watts on its high-intensity filament and 5 watts on its low-intensity filament.
The 1157 uses a BAY15d bayonet base, which features two offset pins at different heights to ensure correct orientation during installation and prevent incorrect seating.
The 1157 conforms to ANSI standards and is recognized across both the United States and Canada, reflecting a standardized specification shared between the two markets.
Because the same bulb number applies to both the front and rear positions, a single replacement part satisfies both fitment requirements on the White/GMC ACM.
The BAY15d base is not interchangeable with single-filament bayonet bases such as the BA15s, as the dual-pin offset configuration is specific to dual-filament applications.