The GMC W4500 Forward uses front and rear turn signal bulbs in sizes 1157, 1073, and 2057. The replacement chart covers vehicle production years spanning 1992 to 2001 with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The three bulb types specified for the GMC W4500 Forward turn signals are the 1157, 1073, and 2057, all of which conform to ANSI standards recognized in the United States and Canada.
The 1157 and 2057 are both dual-filament bulbs sharing the BAY15d bayonet base, while the 1073 is a single-filament bulb fitted with a BA15s bayonet base, making the two base types physically incompatible with each other.
Although the 1157 and 2057 share the same BAY15d base, their wattage ratings differ. The 1157 operates at 21W/5W, whereas the 2057 operates at 26.9W/8W, meaning the 2057 produces a brighter output on both its high and low filaments.
The 1073 is a lower-wattage variant of the 1156 bulb, rated at 13W on a single filament, and its BA15s base is not interchangeable with the BAY15d base found on the 1157 and 2057.
The GMC W4500 Forward (Tiltmaster) used the 1157 bulb for both front and rear turn signals across the 1997-2001 model years.
The Tiltmaster variant used the 1073 bulb for both front and rear turn signals during the 1994-1996 model years.
The 1993 Tiltmaster variant used the 2057 bulb for both front and rear turn signals, placing it as the sole model year to use that bulb exclusively across both positions.
The 1992 model year is the only year in the specifications where two distinct sub-variants are listed, with the Tiltmaster and Medium Duty configurations carrying different bulb sizes depending on the position.
In 1992, the Tiltmaster front and rear turn signals used different bulbs from each other, with the 1073 specified at the front and the 2057 at the rear, both on the Tiltmaster sub-variant.
The 1992 Medium Duty sub-variant used the 2057 for the front turn signal and the 1157 for the rear, both of which use the BAY15d base but differ in filament wattage.