The GMC P60 front side marker requires a 194, 1157, or 168 bulb size, while the rear side marker uses a 194 or 1157 bulb size. The replacement chart covers 1983 to 1990 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 194 bulb is the most frequently specified size across both front and rear side marker positions on the GMC P60, appearing across model years 1983-1990 in various configurations.
The 194 is an ANSI-standard miniature wedge bulb in the T10 form factor, rated at 12V and 3.78W, used in both the US and Canada.
The 1157 is a dual-filament bulb with a BAY15d bayonet base, rated at 12V with a 21W/5W filament split, and it serves a functionally different role than the single-filament 194 wedge bulb.
The 168 bulb shares the same T10 wedge form factor as the 194 but operates at a slightly higher wattage of 4.9W versus 3.78W, making them physically similar but not electrically identical.
On the GMC P60, the front side marker position shows the greatest variation in bulb type, with three distinct sizes specified across the model range: 194, 1157, and 168.
For the 1987 and 1988 front side marker positions, the required bulb depends on headlight configuration: the 1157 applies to standard Medium Duty units, while the 194 applies specifically to those with 2 rectangular headlights.
The same headlight-dependent split applies to the 1983 and 1984 front side marker positions, where the 194 is specified for the 2 rectangular headlight variant while a different bulb applies to the standard Medium Duty configuration.
The rear side marker position on the 1987 P60 specifies the 1157, which stands apart from all other rear side marker years in the specifications, where the 194 is used instead.
The BAY15d bayonet base of the 1157 is physically incompatible with the wedge socket that accepts the 194 and 168, meaning these bulb types are not interchangeable without a socket modification.
The 1985 and 1986 front side marker rows list the 194 without a Medium Duty qualifier, while surrounding years include that designation, reflecting a difference in how those entries are categorized within the specifications.