GMC W6500 Forward Back Up Light Bulb Size

The GMC W6500 Forward back up light utilizes 1073 and 1156 bulb sizes for the lighting components. Available data for the specified vehicle covers the range from 1987 through 1996.

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
1995-1996	1073 (Tiltmaster)
1993-1994	1156 (Tiltmaster)
1991-1992	1156
1988-1990	1156 (Medium Duty)
1988-1990	1073 (Tiltmaster)
1987	1156
1987	1073 (Tiltmaster)

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. Lower wattage variant of 1156. 12V, 13W.	1073
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156

Other Locations

Additional Notes

The two bulb types specified across the GMC W6500 Forward back up light fitments are the 1073 and the 1156, both of which are ANSI-standard single-filament bulbs rated at 12 volts and sharing the same BA15s bayonet base.
The primary distinction between the 1073 and the 1156 lies in wattage. The 1073 is rated at 13W, while the 1156 is rated at 21W, making the 1073 a lower-output variant despite its physical and base compatibility with the 1156.
Because the 1073 and 1156 share the BA15s bayonet base, they are physically interchangeable in terms of fitment, but the wattage difference means substituting one for the other will produce a different light output level than originally specified.
The GMC W6500 Forward (Tiltmaster) uses the 1073 bulb for its back up lights across the 1987-1990 and 1995-1996 model years.
The 1156 bulb is specified for the Medium Duty variant of the W6500 Forward for the 1988-1990 model years.
For 1991-1994, the specifications list only a single bulb size per year with no sub-variant designation, with the 1156 covering 1991-1993 and the 1073 introduced for 1995-1996.
The 1987 model year is notable in that both the 1073 and the 1156 are listed without a Medium Duty sub-variant label on the 1156 entry, unlike the pattern seen in 1988-1990.
The 1994 model year marks the last use of the 1156 in the Tiltmaster sub-variant, as the 1995 and 1996 entries for that sub-variant specify the lower-wattage 1073 instead.