Peterbilt 379 Headlight Bulb Size

Additional Notes

• The Peterbilt 379 (1986-2007) uses four distinct headlamp configurations across its production run: a 2-rectangular-lamp setup, a halogen capsule setup, a 4-rectangular-lamp setup, and, for 1986-1997 models, a 4-round-lamp setup. Each configuration requires a specific bulb type, and these types are not interchangeable with one another.
• The H6054 is a 5x7-inch rectangular sealed beam unit operating at 12V. It serves as both the high beam and low beam bulb in the 2-rectangular-headlamp configuration across all 1986-2007 model years, meaning a single sealed unit handles both functions rather than separate high and low beam bulbs.
• The 9004 is the only non-sealed-beam bulb type in these specifications. It is a dual-filament halogen bulb with a P29t base, rated at 12V with 65W on high beam and 45W on low beam. Its dual-filament design allows one bulb to serve both high and low beam functions in the halogen capsule headlamp configuration.
• Sealed beam units, including the H6054, H4651, H4652, H4656, H5001, and H5006, are not serviceable at the bulb level. When a sealed beam fails, the entire unit requires replacement, as the filament and lens are permanently housed together as one assembly.
• The 4-rectangular-headlamp configuration uses different bulb types for high and low beam functions. The H4651 is specified for high beam use, while the H4652 and H4656 are specified for low beam use depending on the model year. Although the H4651 and H4652 are both 4x6-inch rectangular sealed beam units, they are distinct part numbers and are not listed as interchangeable in these specifications.
• The 4-round-headlamp configuration, present on 1986-1997 models, pairs the H5001 for high beam with 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, making these two types physically incompatible with each other's positions.
• All bulb and sealed beam types listed across these specifications operate at 12V, which is consistent with standard 12-volt electrical systems used in commercial vehicle applications of this type.
• The halogen capsule headlamp configuration uses the 9004 bulb for both high and low beam across all 1986-2007 model years covered in these specifications, making it the only configuration where a single replaceable bulb type is consistent across the entire production span listed.