The GMC G35 front and rear turn signal bulbs utilize 198, 199, and 1156 sizes depending on the specific application and model variant. The replacement chart covers 1970 through 1978 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 GMC G35 uses three distinct bulb types across its front and rear turn signal positions: the 198, 199, and 1156.
The 198 is a T5 miniature wedge bulb rated at 12V and 2W, conforming to ANSI standards for the US and Canadian markets.
The 1156 is a single-filament bulb with a BA15s bayonet base, also rated at 12V but at a significantly higher 21W output, and likewise meets ANSI standards for both markets.
The 199 shares the same BA15s bayonet base and 12V, 21W electrical rating as the 1156, and is classified as a variant of that bulb type under ANSI standards.
The GMC G35 front turn signal uses the 198 bulb across the 1973-1978 model years, while the 1970 and 1971 model years use the higher-wattage 1156.
The 1972 front turn signal position is the only year in the front position to use the 199 bulb, which sits between the 198-equipped years and the earlier 1156-equipped years.
The rear turn signal for the 1973-1978 model years also uses the 198 bulb, matching the front position for those years.
In 1971, the rear turn signal uses the 199 bulb while the front uses the 1156, meaning the two positions are not interchangeable for that year despite both bulbs sharing the BA15s base and identical electrical ratings.
The 199 and 1156 share the same base type and wattage, but they are catalogued as separate part numbers, and substitution between them would depend on physical fitment confirmation beyond their shared electrical specifications.
The 198 wedge bulb at 2W draws considerably less power than the 199 and 1156 at 21W, reflecting a fundamental difference in bulb technology and application between the earlier and later G35 model years covered in these specifications.