Peterbilt 377 Headlight Bulb Size

Additional Notes

• The Peterbilt 377 headlight specifications cover four distinct headlamp configurations across the 1987-2001 model range: a 2-lamp rectangular setup, a 4-lamp rectangular setup, a 4-lamp round setup, and a halogen capsule setup. Each configuration requires a different bulb type, and substituting one for another is not supported by the specifications.
• The H6054 is a 5x7-inch rectangular sealed beam unit operating at 12V. It serves as both the high beam and low beam source in the 2-lamp rectangular configuration, meaning a single unit handles both functions rather than separate dedicated bulbs for each beam mode.
• The 9004 is the only non-sealed-beam bulb type in these specifications. It is a dual-filament halogen bulb rated at 65W for high beam and 45W for low beam, using a P29t base at 12V. Its single-unit, dual-filament design also handles both beam modes within the halogen capsule headlamp configuration.
• The 4-lamp rectangular configuration uses separate bulb types for high and low beam functions. The H4651 is specified for high beam duty, while the low beam position is filled by either the H4656 or H4652 depending on the model year, all of which are 4x6-inch rectangular sealed beam units operating at 12V.
• The H4652 is described as a variant of the H4651, and both share the same 4x6-inch rectangular sealed beam form. Despite their physical similarity, the specifications treat them as distinct part numbers assigned to different beam positions, so they are not interchangeable within the same headlamp assembly.
• The 4-lamp round configuration uses the H5001 for high beam and the H5006 for low beam. The H5001 is a 4-inch square sealed beam unit, while the H5006 is a 5.75-inch round sealed beam unit, meaning the two positions in this configuration take physically different units that cannot be swapped.
• All sealed beam types in these specifications, including the H6054, H4651, H4652, H4656, H5001, and H5006, are replaced as complete units rather than having an internal bulb that is serviced separately. This is a fundamental distinction from the 9004, where only the halogen capsule itself is replaced.
• The 4-lamp round headlamp configuration, which uses the H5001 and H5006, is listed only for the Peterbilt 377 from 1987-1997. The 2-lamp rectangular and halogen capsule configurations span the full 1987-2001 range covered by the specifications.