When doing replacement or upgrading on 1978 – 1987 GMC Caballero, the bulb size guide is necessary for you to take the reference.
Jump to corresponding car model with the catalog bellow.

Low Beam Headlight1982 – 1987 H4656
High Beam Headlight1982 – 1987 H4651
High Beam and Low Beam Headlight1978 – 1981 H6054
Back Up Light1978 – 1987 1156
Brake1978 – 1982 1157
1983 – 1987 2057
Dome Light1978 – 1979 561
Front Side Marker1978 – 1987 194
Front Turn Signal1978 – 1982 1157
1983 – 1987 2057
License Plate1978 – 1987 194
Parking Light1978 – 1979 1157
1980 – 1982 194
1983 – 1987 2057NA
Rear Side Marker1978 – 1979 194
Rear Turn Signal1978 – 1982 1157
1983 – 1987 2057
Tail Light1978 – 1982 1157
1983 – 1987 2057
Courtesy1980 – 1987 561
1978 – 1979 631
Engine Compartment Light1978 – 1979 1003
1980 – 1987 1156
Glove Box1978 – 1987 1895
Radio Display1982 – 1987 194
1980 – 1981 73