The GMC C25 Suburban front and rear turn signal bulb sizes include 198, 1156, and 199 options. The replacement chart covers 1967 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 C25 Suburban uses five distinct bulb types across its front and rear turn signal positions from 1967 through 1978: the 198, 1156, 199, 1073, and 1034.
The 1156 is the most frequently specified bulb across both positions, appearing in multiple model years for both front and rear turn signals. It is a single-filament bulb with a BA15s bayonet base, rated at 12V and 21W.
The 198 is a miniature wedge bulb of the T5 type, rated at 12V and 2W. Its significantly lower wattage compared to the other bulbs in these specifications reflects a fundamentally different bulb construction and socket type.
For the GMC C25 Suburban, the 198 bulb is specified for both the front and rear turn signal positions across the 1973-1978 model years.
The 199 shares the same BA15s bayonet base and 12V/21W rating as the 1156 and is classified as a variant of it. Despite this similarity, the front and rear positions do not use them interchangeably within the same model year on this vehicle.
The 1073 is a lower wattage variant of the 1156, using the same BA15s bayonet base but rated at 13W rather than 21W. It is specified for both the front and rear turn signal positions on the 1968 model year.
The 1034 is a dual-filament bulb with a BAY15d bayonet base, rated at 12V and 21/5W. Its BAY15d base differs from the BA15s base used by the 1156, 199, and 1073, making these types physically non-interchangeable despite their outward similarity.
The 1034 is specified exclusively for the rear turn signal of the 1967 model year, while the front turn signal of that same year uses the single-filament 1156.
All bulb types in these specifications conform to ANSI standards applicable in both the United States and Canada.
The front and rear turn signal positions share the same bulb type in most model years, though the 1970 and 1971 model years are exceptions, with differing bulb types between the two positions.