Isuzu FTR 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, mounted on a P43t base. Because it carries both filaments in a single housing, the Isuzu FTR Tilt Cab (2006-2011) uses the same 9003 bulb for both the high beam and low beam positions.
• The H4651 and H4656 are rectangular sealed beam units following the 4x6-inch ANSI standard. In a sealed beam design, the reflector, lens, and filament are fused into one glass unit, so the entire assembly is replaced rather than an internal bulb alone.
• The H4651 handles the high beam function and the H4656 handles the low beam function on the 1988-2005 FTR. Although both share the same 4x6-inch rectangular form factor and 12V rating, they are not interchangeable due to differing beam patterns and filament positions specific to each function.
• The 2006-2011 Tilt Cab configuration represents a distinct fitment group within the FTR lineup, as those model years use the 9003 halogen bulb rather than sealed beam units, reflecting a different headlight housing design from earlier production years.
• The 9003 bulb type is defined under ANSI standards applicable to the United States and Canada, as are the H4651 and H4656 sealed beam units, meaning all three types conform to North American lighting standardization requirements.
• Because the H4651 and H4656 units share the same physical 4x6-inch rectangular format, there is a risk of incorrect substitution. However, installing an H4656 in a high beam position or an H4651 in a low beam position would result in an improper beam pattern, as each unit is engineered for its designated function.
• The 9003 bulb's P43t base is a standardized bayonet-style fitting. Replacement bulbs must match this base type to seat correctly in the Tilt Cab headlight socket used across the 2006-2011 model years.
• Across the full 1988-2011 production span covered by these specifications, the Isuzu FTR uses three distinct bulb types in total: the H4651 for high beam, the H4656 for low beam, and the 9003 serving both functions in the Tilt Cab variant.