GMC W4500 Forward Headlight Bulb Size

The GMC W4500 Forward headlight bulb size specifications include high beam options of H4651, H5001, and H6054, along with low beam sizes of H4656, H5006, and H6054 for this commercial vehicle model. The replacement chart covers 1992 through 2001 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.

High Beam Headlight

Years	Bulb Size
1997-2001	H4651 (Tiltmaster)
1996	H5001 (Tiltmaster)
1992-1995	H5001 (Tiltmaster)
	H6054 (With 2 Rectangular Headlamps)
	H6024 (With 2 Round Headlamps)
	H4651 (With 4 Rectangular Headlamps)

Low Beam Headlight

Years	Bulb Size
1997-2001	H4656 (Tiltmaster)
1996	H5006 (Tiltmaster)
1992-1995	H5006 (Tiltmaster)
	H6054 (With 2 Rectangular Headlamps)
	H6024 (With 2 Round Headlamps)
	H4656 (With 4 Rectangular Headlamps)

Bulb Specifications

Description	Bulb Size
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). 4-inch square sealed beam unit. Not a replaceable bulb — the entire unit is replaced. 12V.	H5001
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.	H4656
ANSI standard (US & Canada). 5.75-inch round sealed beam unit. Not a replaceable bulb — the entire unit is replaced. 12V.	H5006

Other Locations

Additional Notes

All headlight bulb types listed for the GMC W4500 Forward across both high beam and low beam positions are sealed beam units, meaning the entire lens-and-filament assembly is replaced as a single unit rather than a separate bulb being swapped within a housing.
Every sealed beam type in these specifications operates at 12V and conforms to ANSI standards recognized in both the United States and Canada.
The H4651 and H4656 are both 4x6-inch rectangular sealed beam units, with the H4651 serving the high beam position and the H4656 serving the low beam position. These two types are not interchangeable despite sharing the same physical form factor, as each is rated for a distinct beam function.
The Tiltmaster variant of the GMC W4500 Forward used H5001 (high beam) and H5006 (low beam) sealed beam units from 1992-1996, then transitioned to H4651 (high beam) and H4656 (low beam) from 1997-2001.
The H5001 is a 4-inch square sealed beam unit, while the H5006 is a 5.75-inch round sealed beam unit. Although both served the Tiltmaster variant simultaneously as high and low beam units respectively, their physical forms are entirely different and are not interchangeable.
The non-Tiltmaster configurations of the W4500 Forward from 1992-1995 required different bulb types depending on whether the vehicle was fitted with a 2-headlamp or 4-headlamp system. The 4-rectangular-headlamp configuration used H4651 and H4656, while the 2-rectangular-headlamp configuration used H6054 for both beam positions.
The H6024 is a 7-inch round sealed beam unit used in both high and low beam positions on the 2-round-headlamp configuration from 1992-1995. The H6054 is a 5x7-inch rectangular sealed beam unit serving the same dual-beam role in the 2-rectangular-headlamp configuration during the same years.
The 1995 model year carried the widest range of bulb fitments across all variants, with four distinct high beam types and four distinct low beam types listed, reflecting the coexistence of Tiltmaster and multiple non-Tiltmaster headlamp configurations in that year.