Isuzu NPR-HD Headlight Bulb Size

Additional Notes

• The 9003 bulb is a dual-filament halogen type rated at 12V with a 60W high beam filament and a 55W low beam filament, fitted with a P43t base. Because it contains both filaments in a single unit, the Isuzu NPR-HD Tilt Cab uses the same 9003 bulb for both high and low beam positions across the 2006-2013 model years.
• The H4651 and H4656 are 4x6-inch rectangular sealed beam units operating at 12V. Unlike the 9003, neither type houses a replaceable bulb inside; the entire sealed unit is the light source and must be replaced as a whole when it fails.
• The H4651 serves the high beam position and the H4656 serves the low beam position on the NPR-HD from 1999-2005. Although both are 4x6-inch rectangular sealed beam units, they are not interchangeable with each other due to differing beam patterns optimized for their respective functions.
• A configuration change occurred between the 2005 and 2006 model years on the Isuzu NPR-HD Tilt Cab. The sealed beam H4651 and H4656 units used through 2005 were replaced by the 9003 halogen bulb starting in 2006, representing a shift from sealed beam to replaceable bulb technology.
• The 9003 bulb is functionally equivalent to the H4 bulb used in many international markets, though the 9003 designation follows the ANSI standard applicable in the United States and Canada, which is the standard under which these specifications are listed.
• The Tilt Cab body style notation appears consistently across all years in the specifications, indicating that the listed bulb sizes apply specifically to that cab configuration of the NPR-HD.