GMC W5500 Forward Back Up Light Bulb Size

The GMC W5500 Forward back up light utilizes 1156 and 1073 bulb sizes for the rear illumination system. Available data for the specific components covers the range from 1988 through 2001.

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
1997-2001	1156 (Tiltmaster)
1994-1996	1073 (Tiltmaster)
1993	1156 (Tiltmaster)
1992	1156
1991	1156 (Medium Duty)
1991	1073 (Tiltmaster)
1989-1990	1156
1988	1156 (Medium Duty)
1988	1073 (Tiltmaster)

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. Lower wattage variant of 1156. 12V, 13W.	1073

Other Locations

Additional Notes

The back up light bulb specifications for the GMC W5500 Forward span model years 1988 through 2001, with all entries carrying either a 1156 or 1073 bulb designation.
Both the 1156 and 1073 are ANSI-standard single-filament bulbs sharing the same BA15s bayonet base and a 12-volt operating voltage, which means they are physically interchangeable in terms of socket fitment.
The key electrical difference between the two types is wattage. The 1156 operates at 21 watts, while the 1073 operates at 13 watts, making them non-equivalent in light output despite their identical base configuration.
The 1156 bulb is the more widely specified of the two across the W5500 Forward range, appearing in the 1988 Medium Duty, 1989-1990, 1991 Medium Duty, 1992-1993, and 1997-2001 Tiltmaster entries.
The 1073 bulb is specified for the GMC W5500 Forward Tiltmaster sub-variant in 1988, 1991, and 1994-1996, indicating that the Tiltmaster configuration used the lower-wattage option during those years.
In model year 1991, the W5500 Forward carried two separate back up light bulb specifications simultaneously, with the Medium Duty variant requiring a 1156 and the Tiltmaster requiring a 1073, reflecting distinct electrical configurations within the same model year.
The same dual-specification pattern also occurs in 1988, where the Medium Duty variant takes a 1156 and the Tiltmaster takes a 1073, establishing that this sub-variant distinction was present at both ends of the production span covered by these specifications.
From 1993 onward, the Tiltmaster designation transitions from the 1073 to the 1156 bulb, with 1993 itself already listed under the 1156 specification, while 1994-1996 revert to the 1073 before the 1156 returns from 1997 through 2001.
Because the 1156 and 1073 share the BA15s bayonet base, substituting one for the other is physically possible, but the wattage difference means the replacement would not match the original electrical specification of the vehicle.