When doing replacement or upgrading on 1964 – 1996 GMC G1500 G2500 G3500 2 4 headlamps rectangular round with, the bulb size guide is necessary for you to take the reference.
Jump to corresponding car model with the catalog bellow.

Low Beam Headlight 1988 – 1991 H4656
1992 – 1995 H4703
1964 – 1965 H5006
High Beam Headlight 1988 – 1991 H4651
1992 – 1995 H4701
1964 – 1965 H5001
Back Up Light 1988 – 1995 1156
Brake 1965 1034
1964 1157
1988 – 1995 2057
Dome Light 1964 – 1965, 1988 – 1994 211-2
1995 578
Front Side Marker 1988 – 1995 194
Front Turn Signal 1988 – 1991 2057
1992 – 1994 3157
License Plate 1995 194
1988 – 1994 67
Parking Light 1988 – 1991 2057NA
1992 – 1995 3157
1964 – 1965 67
Rear Turn Signal 1988 – 1995 2057
Tail Light 1964 – 1965 1157
1988 – 1995 2057
Front Inner Turn Signal 1995 3157
Front Outer Turn Signal 1995 194NA
Center High Mount Stop Light 1988 – 1995 921
Courtesy 1995 212-2
Engine Compartment Light 1992 – 1995 12814
Map Light 1995 906
1992 – 1994 912
Radio Display 1992 – 1995 1893
High Beam and Low Beam Headlight 1964 – 1965 6014
1988 – 1995 H6054
Back Up Light 1988 – 1995 1156
Brake 1964 – 1965 1157
1988 – 1995 2057
Dome Light 1964 – 1965, 1988 – 1994 211-2
1995 578
Front Side Marker 1988 – 1995 194
Front Turn Signal 1988 – 1991 2057NA
1992 – 1994 3157
License Plate 1995 194
1988 – 1994 67
Parking Light 1988 – 1991 2057NA
1992 – 1995 3157
1964 – 1965 67
Rear Turn Signal 1988 – 1995 2057
Tail Light 1964 – 1965 1157
1988 – 1995 2057
Front Inner Turn Signal 1995 3157
Front Outer Turn Signal 1995 194NA
Center High Mount Stop Light 1988 – 1995 921
Courtesy 1995 212-2
Engine Compartment Light 1992 – 1995 12814
Map Light 1995 906
1992 – 1994 912
Radio Display 1992 – 1995 1893
Low Beam Headlight 1966 H5006
High Beam Headlight 1966 H5001
High Beam and Low Beam Headlight 1985 – 1987 H6024
1979, 1981 – 1984 H6054
Back Up Light 1979, 1981 – 1987 1156
Brake 1966, 1979, 1981 – 1982 1157
1983 – 1987 2057
Dome Light 1966, 1981 – 1984 211-2
1979, 1985 – 1987 578
Front Side Marker 1979, 1985 – 1987 168
1982 – 1984 194
1981 68
Front Turn Signal 1966 1156
1979 1157
1981 – 1982 1157NA
1985 – 1987 2057
1983 – 1984 2057NA
License Plate 1979, 1981 – 1987 67
Parking Light 1979, 1981 – 1982 1157
1983 – 1987 2057NA
1966 67
Rear Side Marker 1979 67
Rear Turn Signal 1966 1156
1979, 1981 – 1982 1157
1983 – 1987 2057
Tail Light 1966, 1979, 1981 – 1982 1157
1983 – 1987 2057
Courtesy 1983 – 1987 212-2
1979 93
Map Light 1985 – 1987 906
Radio Display 1985 – 1987 1893
High Beam and Low Beam Headlight 1980 6014
Back Up Light 1980 1156
Brake 1980 1157
Dome Light 1980 211-2
Front Side Marker 1980 194
Front Turn Signal 1980 1157
License Plate 1980 67
Parking Light 1980 1157
Rear Turn Signal 1980 1157
Tail Light 1980 1157
High Beam and Low Beam Headlight 1980 H6054
Back Up Light 1980 1156
Brake 1980 1157
Dome Light 1980 211-2
Front Side Marker 1980 194
Front Turn Signal 1980 1157NA
License Plate 1980 67
Parking Light 1980 1157
Rear Turn Signal 1980 1157
Tail Light 1980 1157
Low Beam Headlight 1988 – 1991 H4656
1992 – 1995 H4703
High Beam Headlight 1988 – 1991 H4651
1992 – 1995 H4701
Back Up Light 1988 – 1995 1156
Brake 1988 – 1995 2057
Dome Light 1988 – 1994 211-2
1995 578
Front Side Marker 1988 – 1995 194
Front Turn Signal 1988 – 1991 2057
1992 – 1994 3157
License Plate 1995 194
1988 – 1994 67
Parking Light 1988 – 1991 2057NA
1992 – 1995 3157
Rear Turn Signal 1988 – 1995 2057
Tail Light 1988 – 1995 2057
Front Inner Turn Signal 1995 3157
Front Outer Turn Signal 1995 194NA
Center High Mount Stop Light 1988 – 1995 921
Courtesy 1995 212-2
Engine Compartment Light 1992 – 1995 12814
Map Light 1995 906
1992 – 1994 912
Radio Display 1992 – 1995 1893
High Beam and Low Beam Headlight 1988 – 1995 H6054
Back Up Light 1988 – 1995 1156
Brake 1988 – 1995 2057
Dome Light 1988 – 1994 211-2
1995 578
Front Side Marker 1988 – 1995 194
Front Turn Signal 1988 – 1991 2057NA
1992 – 1994 3157
License Plate 1995 194
1988 – 1994 67
Parking Light 1988 – 1991 2057NA
1992 – 1995 3157
Rear Turn Signal 1988 – 1995 2057
Tail Light 1988 – 1995 2057
Front Inner Turn Signal 1995 3157
Front Outer Turn Signal 1995 194NA
Center High Mount Stop Light 1988 – 1995 921
Courtesy 1995 212-2
Engine Compartment Light 1992 – 1995 12814
Map Light 1995 906
1992 – 1994 912
Radio Display 1992 – 1995 1893
High Beam and Low Beam Headlight 1985 – 1987 H6024
1979, 1981 – 1984 H6054
Back Up Light 1979, 1981 – 1987 1156
Brake 1979, 1981 – 1982 1157
1983 – 1987 2057
Dome Light 1981 – 1984 211-2
1979, 1985 – 1987 578
Front Side Marker 1979, 1985 – 1987 168
1982 – 1984 194
1981 68
Front Turn Signal 1979 1157
1981 – 1982 1157NA
1985 – 1987 2057
1983 – 1984 2057NA
License Plate 1979, 1981 – 1987 67
Parking Light 1979, 1981 – 1982 1157
1983 – 1987 2057NA
Rear Side Marker 1979 67
Rear Turn Signal 1979, 1981 – 1982 1157
1983 – 1987 2057
Tail Light 1979, 1981 – 1982 1157
1983 – 1987 2057
Courtesy 1983 – 1987 212-2
1979 93
Map Light 1985 – 1987 906
Radio Display 1985 – 1987 1893
High Beam and Low Beam Headlight 1980 6014
Back Up Light 1980 1156
Brake 1980 1157
Dome Light 1980 211-2
Front Side Marker 1980 194
Front Turn Signal 1980 1157
License Plate 1980 67
Parking Light 1980 1157
Rear Turn Signal 1980 1157
Tail Light 1980 1157
High Beam and Low Beam Headlight 1980 H6054
Back Up Light 1980 1156
Brake 1980 1157
Dome Light 1980 211-2
Front Side Marker 1980 194
Front Turn Signal 1980 1157NA
License Plate 1980 67
Parking Light 1980 1157
Rear Turn Signal 1980 1157
Tail Light 1980 1157
Low Beam Headlight 1988 – 1991 H4656
1992 – 1996 H4703
High Beam Headlight 1988 – 1991 H4651
1992 – 1996 H4701
Back Up Light 1988 – 1996 1156
Brake 1988 – 1996 2057
Dome Light 1988 – 1994 211-2
1995 – 1996 578
Front Side Marker 1988 – 1996 194
Front Turn Signal 1988 – 1991 2057
1992 – 1994 3157
License Plate 1995 – 1996 194
1988 – 1994 67
Parking Light 1988 – 1991 2057NA
1992 – 1996 3157
Rear Turn Signal 1988 – 1996 2057
Tail Light 1988 – 1996 2057
Front Inner Turn Signal 1995 – 1996 3157
Front Outer Turn Signal 1995 – 1996 194NA
Center High Mount Stop Light 1988 – 1996 921
Courtesy 1995 – 1996 212-2
Engine Compartment Light 1992 – 1996 12814
Map Light 1995 – 1996 906
1992 – 1994 912
Radio Display 1992 – 1996 1893
High Beam and Low Beam Headlight 1988 – 1996 H6054
Back Up Light 1988 – 1996 1156
Brake 1988 – 1996 2057
Dome Light 1988 – 1994 211-2
1995 – 1996 578
Front Side Marker 1988 – 1996 194
Front Turn Signal 1988 – 1991 2057NA
1992 – 1994 3157
License Plate 1995 – 1996 194
1988 – 1994 67
Parking Light 1988 – 1991 2057NA
1992 – 1996 3157
Rear Turn Signal 1988 – 1996 2057
Tail Light 1988 – 1996 2057
Front Inner Turn Signal 1995 – 1996 3157
Front Outer Turn Signal 1995 – 1996 194NA
Center High Mount Stop Light 1988 – 1996 921
Courtesy 1995 – 1996 212-2
Engine Compartment Light 1992 – 1996 12814
Map Light 1995 – 1996 906
1992 – 1994 912
Radio Display 1992 – 1996 1893
High Beam and Low Beam Headlight 1985 – 1987 H6024
1979, 1981 – 1984 H6054
Back Up Light 1979, 1981 – 1987 1156
Brake 1979, 1981 – 1982 1157
1983 – 1987 2057
Dome Light 1981 – 1984 211-2
1979, 1985 – 1987 578
Front Side Marker 1979, 1985 – 1987 168
1982 – 1984 194
1981 68
Front Turn Signal 1979 1157
1981 – 1982 1157NA
1985 – 1987 2057
1983 – 1984 2057NA
License Plate 1979, 1981 – 1987 67
Parking Light 1979, 1981 – 1982 1157
1983 – 1987 2057NA
Rear Side Marker 1979 67
Rear Turn Signal 1979, 1981 – 1982 1157
1983 – 1987 2057
Tail Light 1979, 1981 – 1982 1157
1983 – 1987 2057
Courtesy 1983 – 1987 212-2
1979 93
Map Light 1985 – 1987 906
Radio Display 1985 – 1987 1893
High Beam and Low Beam Headlight 1980 6014
Back Up Light 1980 1156
Brake 1980 1157
Dome Light 1980 211-2
Front Side Marker 1980 194
Front Turn Signal 1980 1157
License Plate 1980 67
Parking Light 1980 1157
Rear Turn Signal 1980 1157
Tail Light 1980 1157
High Beam and Low Beam Headlight 1980 H6054
Back Up Light 1980 1156
Brake 1980 1157
Dome Light 1980 211-2
Front Side Marker 1980 194
Front Turn Signal 1980 1157NA
License Plate 1980 67
Parking Light 1980 1157
Rear Turn Signal 1980 1157
Tail Light 1980 1157