The Chevrolet P40 front side marker uses a 1157 bulb size, while rear side marker applications accommodate either 194 or 1157 bulb sizes. The replacement chart covers 1979 through 1988 production 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 Chevrolet P40 front side marker position uses the 1157 bulb across all listed model years from 1979-1988, making it the only bulb type specified for that position throughout the entire documented range.
The 1157 is a dual-filament bulb with a BAY15d bayonet base, rated at 12V with a 21W/5W output, and is classified under the ANSI standard applicable in both the US and Canada.
The dual-filament design of the 1157 means it houses two separate filaments within a single envelope, each operating at a different wattage, which is a common characteristic of bulbs serving combined stop and tail or marker functions.
The rear side marker position on the P40 uses the 194 bulb for most of the listed years, specifically 1979-1984 and 1988.
The 194 is a miniature wedge-style T10 bulb rated at 12V and 3.78W, also conforming to the ANSI standard for the US and Canadian markets.
The rear side marker on the Chevrolet P40 for 1986-1987 uses the 1157 rather than the 194, which represents a departure from the bulb type used in the surrounding model years for that same position.
Because the 1157 and 194 are not interchangeable, the rear side marker socket type on the P40 differs between the 1986-1987 models and the other listed years, as the 1157 uses a BAY15d bayonet base while the 194 uses a wedge-style base.
The significant wattage difference between the 1157 (21W/5W) and the 194 (3.78W) means substituting one for the other in the rear side marker position would result in incorrect light output and potential electrical incompatibility.
The 1157 is the dominant bulb type across both positions when considering the full set of specifications, appearing in all ten front side marker entries and in two of the ten rear side marker entries.
The 194 bulb, while lower in wattage than the 1157, is a widely used miniature automotive bulb, and its T10 wedge base format is a standard fitment found across many low-current lighting applications.