Peterbilt 320 Headlight Bulb Size

Additional Notes

• The H4651 is the most widely specified high beam bulb across the Peterbilt 320 range, appearing as the sole high beam fitment for the 2011-2017 model years and as one of three options for the 4-rectangular-headlamp configuration from 1987-2009. It is a sealed-beam unit conforming to the 4x6-inch rectangular format, a standard that was widely adopted in North American commercial vehicle lighting.
• The 9004 bulb is a dual-filament halogen capsule type, meaning a single bulb serves both high and low beam functions within the same housing. On the Peterbilt 320, it is specified for vehicles equipped with halogen capsule headlamps across the full 1987-2009 span of that headlamp configuration, covering both high and low beam positions simultaneously.
• The H6054 is a sealed-beam rectangular unit specified for the 2-rectangular-headlamp configuration on the 320 from 1987-2009. Because only two lamps are present in that setup, the H6054 handles both high and low beam output from a single sealed unit per side, which is a characteristic of certain sealed-beam designs that incorporate dual filaments.
• The H4656 and H4652 are both 4x6-inch rectangular sealed-beam bulbs differentiated by their beam pattern: the H4651 and H4656 are associated with high and low beam roles respectively in paired systems, while the H4652 also serves as a low beam unit. On the Peterbilt 320, the low beam position in the 4-rectangular-headlamp configuration is filled by either the H4656 or H4652 depending on the specific model year, and these two types are not interchangeable despite their physical similarity.
• The H5001 and H5006 are round sealed-beam bulbs specified for the 4-round-headlamp configuration, which is listed only for the 1987-1997 model years. The H5001 fills the high beam position and the H5006 fills the low beam position in that arrangement. Round sealed beams of this type conform to the 5.75-inch circular format used in traditional multi-lamp headlamp systems.
• The Peterbilt 320 headlamp system is headlamp-configuration-dependent, meaning the correct bulb type is determined not solely by model year but also by which of the three headlamp configurations is installed: 2 rectangular lamps, 4 rectangular lamps, or halogen capsule lamps. For the 1987-2009 range, all three configurations were available concurrently within the same model year, requiring confirmation of the installed headlamp type before a replacement bulb is selected.
• The 4-round-headlamp configuration, which uses the H5001 for high beam and H5006 for low beam, is listed only through 1997. From 1998 onward, the specifications no longer include that configuration, leaving only the 2-rectangular, 4-rectangular, and halogen capsule options for subsequent years in the 1987-2009 range.
• From 2011 onward, the specifications list only a single bulb type per beam position: H4651 for high beam and H4656 for low beam, with no headlamp-configuration variants noted. This reflects a consolidation to a single headlamp system for those model years on the 320.
• The H4651 and H4656 are physically similar sealed-beam units of the same 4x6-inch rectangular format but are calibrated for different beam patterns, high and low beam respectively. Substituting one for the other would result in incorrect beam projection and is not supported by the fitment data in these specifications.
• The 9004 bulb uses a two-filament design within a single halogen capsule, which distinguishes it from the sealed-beam types also listed for the same model years. Because the 9004 integrates both beam functions into one replaceable capsule rather than a sealed reflector unit, it is not physically or electrically interchangeable with any of the H-series sealed-beam bulbs listed in these specifications.