GMC P25 / P2500 front and rear turn signal bulbs utilize sizes 1156, 1034, 1073, and 199 depending on application and model year. The replacement chart covers 1967 to 1972 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 1156 bulb is the most frequently specified type across these turn signal positions, appearing in the front turn signal for 1969-1972 and in the rear turn signal for 1970 and 1972.
The 1156 is a single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base, which is a single-contact base with a 15mm collar.
The GMC P25 / P2500 front turn signal used three different bulb types across the 1967-1972 model years, with the 1073 specified for 1967, the 1034 for 1968, and the 1156 for 1969-1972.
The rear turn signal shows greater variation than the front, with the 199 bulb specified for 1969 and 1971 while the 1156 covers 1970 and 1972, despite both the 199 and 1156 sharing identical electrical ratings of 12V and 21W.
Although the 199 and 1156 share the same BA15s bayonet base and 12V, 21W rating, they carry distinct ANSI designations, and substitution between them should be confirmed against fitment requirements before use.
The 1034 bulb, specified for both the front and rear turn signals in 1968, is a dual-filament type rated at 12V and 21/5W, using a BAY15d bayonet base. The BAY15d base has offset pins to prevent incorrect insertion, distinguishing it physically from the single-filament BA15s base used by the other bulb types in these specifications.
Because the 1034 uses a BAY15d base and the 1156, 1073, and 199 all use a BA15s base, these types are not physically interchangeable with one another.
The 1073 bulb, specified for both front and rear positions in 1967, is a single-filament BA15s type rated at 12V and 13W, making it a lower-wattage variant of the 1156. The reduced wattage means it produces less light output than the 1156 despite sharing the same base type.
The 1034 is described as a variant of the 1157, which is a widely used dual-filament automotive bulb. The 1034 differs from the 1157 in wattage output on one of its filaments, so the two are not rated as direct replacements for each other.
All four bulb types in these specifications, the 1156, 1034, 1073, and 199, conform to ANSI standards applicable in both the United States and Canada.