The Mack CH front and rear turn signal bulb size is 1157 for this truck model. The replacement chart covers vehicle production years spanning 1989 to 1997.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mack CH uses the 1157 bulb type for both its front and rear turn signals across all listed model years from 1989-1997.
The 1157 is an ANSI-standardized bulb type recognized across the United States and Canada, meaning it conforms to a defined set of electrical and physical characteristics shared by all compliant manufacturers.
The 1157 is a dual-filament bulb, which means it contains two separate filaments within a single housing, allowing it to serve two distinct lighting functions from one unit.
The bulb operates on a 12-volt electrical system, consistent with the standard automotive and commercial vehicle electrical architecture of that era.
Its two filaments are rated at 21 watts and 5 watts respectively, where the higher-wattage filament typically handles the brighter turn signal or stop function, and the lower-wattage filament handles a reduced-intensity function such as a running or parking light.
The 1157 uses a BAY15d bayonet base, which is a two-pin offset bayonet mount. The offset pin placement is a deliberate design feature that prevents the bulb from being inserted in the wrong orientation, ensuring each filament connects to its correct circuit.
Because the BAY15d base has offset pins, it is not physically interchangeable with single-pin bayonet bases such as the BA15s, even when the overall housing size appears similar.
The uniform use of the 1157 across both front and rear positions for all listed years means a single bulb type covers all four turn signal sockets on the vehicle throughout the 1989-1997 production span.