GMC P4500 Headlight Bulb Size

The GMC P4500 headlight bulb specifications include high beam sizes H6054, H6024, and H4651, along with low beam sizes H6054, H6024, and H4656 for the front lighting assembly. A replacement chart documents bulb size data spanning 1979 to 1990 for this vehicle model.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

High Beam Headlight

Years	Bulb Size
1989-1990	H6054
1979-1988	H6054 (With 2 Rectangular Headlamps)
	H6024 (With 2 Round Headlamps)
	H4651 (With 4 Rectangular Headlamps)

Low Beam Headlight

Years	Bulb Size
1989-1990	H6054
1979-1988	H6054 (With 2 Rectangular Headlamps)
	H6024 (With 2 Round Headlamps)
	H4656 (With 4 Rectangular Headlamps)

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). 5x7-inch rectangular sealed beam unit. Not a replaceable bulb — the entire unit is replaced. 12V.	H6054
ANSI standard (US & Canada). 7-inch round sealed beam unit. Not a replaceable bulb — the entire unit is replaced. 12V.	H6024
ANSI standard (US & Canada). 4x6-inch rectangular sealed beam unit. Not a replaceable bulb — the entire unit is replaced. 12V.	H4651
ANSI standard (US & Canada). 4x6-inch rectangular sealed beam unit. Not a replaceable bulb — the entire unit is replaced. 12V.	H4656

Other Locations

Additional Notes

The GMC P4500 uses three distinct sealed beam headlamp types across its model range: the H6054, H6024, and, depending on beam function, either the H4651 or H4656. All four types are ANSI-standardized units rated at 12V and are sold and used throughout the United States and Canada.
All headlamp types fitted to the P4500 are sealed beam units, meaning the lens, reflector, and filament are fused into a single assembly. When a filament fails, the entire unit requires replacement rather than an individual bulb.
The H6054 is a 5x7-inch rectangular sealed beam. It serves as both the high beam and low beam unit on 2-rectangular-headlamp configurations across the 1979-1990 model years, functioning as a dual-beam lamp in a two-lamp system.
The H6024 is a 7-inch round sealed beam unit. It fills both the high beam and low beam positions on 2-round-headlamp configurations for the 1979-1988 model years, also operating as a dual-beam lamp.
On 4-rectangular-headlamp configurations for the 1979-1988 model years, the high beam and low beam positions use different bulb types. The H4651 occupies the high beam position, while the H4656 occupies the low beam position. Both are 4x6-inch rectangular sealed beam units, but they are not interchangeable between positions.
The physical similarity between the H4651 and H4656 presents a fitment risk. Both share the same 4x6-inch rectangular sealed beam format, but each is engineered for a specific beam function. Installing one in place of the other on a 4-lamp system would place the wrong beam pattern in the wrong position.
For the 1989-1990 model years, the specifications list only the H6054 for both high beam and low beam, with no headlamp configuration qualifiers noted. This indicates those model years were equipped solely with the 2-rectangular-headlamp arrangement.
The H6054 is the most broadly applied unit across the P4500 specifications, covering all 1979-1990 high beam and low beam positions on 2-rectangular-headlamp vehicles, making it the most frequently referenced sealed beam type in this fitment data.