GMC G15 front and rear turn signal bulbs utilize 198, 1156, and 199 sizes depending on production specifications. The replacement chart covers 1967 through 1978 model years with corresponding bulb size data.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC G15 front and rear turn signals used five distinct bulb types across the 1967-1978 model years: the 198, 1156, 199, 1034, and 1073.
The 198 is a T5 miniature wedge bulb rated at 12V and 2W, making it significantly lower in wattage than the other bulb types specified for the GMC G15.
The 198 bulb was the most frequently specified type across the G15 turn signal data, appearing in both the front and rear positions for the 1973-1978 model years.
The 199 and 1156 are both single-filament bulbs with a BA15s bayonet base rated at 12V and 21W, with the 199 classified as a variant of the 1156. These two types are electrically equivalent but are not always interchangeable due to potential physical differences in the base or envelope.
The front turn signal used the 1156 in 1972 while the rear used the 199 that same year, meaning the front and rear positions required different bulbs despite sharing the same wattage rating.
The 1073 is a single-filament bulb with a BA15s bayonet base rated at 12V and 13W, described as a lower wattage variant of the 1156. Substituting a 1156 for a 1073 would introduce a higher wattage draw than originally specified.
The 1034 is a dual-filament bulb with a BAY15d bayonet base rated at 12V and 21/5W, and is a variant of the 1157. Its BAY15d base is physically distinct from the BA15s base used by the 1156, 199, and 1073, making these types non-interchangeable.
The 1034 appeared only in the 1968 front turn signal position, making it the least common bulb type in the G15 specifications and the only dual-filament type listed.
The 1073 appeared in both the front and rear turn signal positions for the 1967 model year and in the rear position for the 1968 model year, after which it was no longer specified for the G15.