The Chevrolet P40 front turn signal bulb size measures 1157 or 2057, while the rear turn signal bulb size measures 1157. The replacement chart covers vehicle production spanning 1979 to 1988.
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 Chevrolet P40 specifications, appearing in both the front and rear turn signal positions for the 1979-1983 and 1985-1988 model years, as well as all rear turn signal positions from 1979-1988.
The 1157 is a dual-filament bulb operating at 12 volts with a BAY15d bayonet base, rated at 21W on the high filament and 5W on the low filament, conforming to ANSI standards recognized in both the United States and Canada.
The dual-filament design of the 1157 allows a single bulb to serve two lighting functions, typically combining the turn signal function on the high-wattage filament with a lower-intensity running or parking light function on the low-wattage filament.
The 2057 bulb was specified for the front turn signal position on the Chevrolet P40 for the 1983-1984 model years only, while the rear turn signal retained the 1157 for those same years.
The 2057 shares the same BAY15d bayonet base and 12-volt operating voltage as the 1157, making the two bulbs physically compatible in terms of socket fitment.
Despite the shared base type, the 2057 draws notably more power than the 1157, rated at 26.9W on the high filament and 8W on the low filament, which classifies it as the brighter of the two bulbs.
Because the 1157 and 2057 share the BAY15d base, one may physically seat in a socket intended for the other, but the difference in wattage ratings means substituting one for the other could affect light output and potentially circuit load.
The rear turn signal position on the Chevrolet P40 used the 1157 uniformly across all ten model years covered in the specifications, from 1979 through 1988, with no variation.