GMC K35 Back Up Light Bulb Size

The GMC K35 back up light bulb size chart specifies 1156 and 199 bulb sizes for this vehicle model. The replacement chart covers 1973 to 1978 production 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.

Bulb Size by Year Range

Years	Bulb Size
1978	1156
1977	199
1973-1974	1156

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. Variant of 1156. 12V, 21W.	199

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Additional Notes

The GMC K35 back up light specifications reference two bulb types across the listed model years: the 1156 and the 199.
Both the 1156 and the 199 are ANSI-standard bulbs recognized in the US and Canada, each operating at 12 volts and 21 watts with a single filament.
The BA15s bayonet base is shared by both bulb types, featuring a single contact pin on a 15mm base, which is a common automotive base style designed for straightforward insertion and rotation to lock into the socket.
The 199 is a variant of the 1156, meaning the two share the same electrical ratings and base configuration while being catalogued under distinct ANSI part numbers.
The 1156 is specified for the GMC K35 in 1973, 1974, and 1978, making it the more frequently listed bulb across the available model years.
The 199 is specified for the 1977 model year, representing the sole year in the dataset where that bulb number is called out instead of the 1156.
Because the 199 is a variant of the 1156 with identical voltage, wattage, and base type, the two are electrically and physically interchangeable in applications where socket fitment is compatible.
Single-filament construction in both bulb types means each serves one dedicated lighting function, which in this context is the back up light circuit only, with no secondary filament for additional functions such as braking.