The Isuzu FRR uses an H4651 bulb size for high beam headlights and an H4656 bulb size for low beam headlights. The replacement chart covers vehicle production years spanning 1996 to 2004.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Isuzu FRR Tilt Cab uses the H4651 sealed beam unit for high beam headlights across the 1996-2004 model years, with 1999 absent from the listed data.
The H4651 and H4656 are both ANSI-standardized 4x6-inch rectangular sealed beam units operating at 12V, a format common in North American commercial vehicle lighting.
The H4656 sealed beam unit serves the low beam headlight position in the Isuzu FRR Tilt Cab across the same 1996-2004 span covered by the specifications.
Both the H4651 and H4656 are sealed beam units, meaning the lens, reflector, and filament are fused into a single assembly. When the filament fails, the entire unit requires replacement rather than an internal bulb swap.
The H4651 and H4656 share the same 4x6-inch rectangular form factor and voltage rating, but they are not interchangeable. Each is designated for a specific beam function, high or low, and substituting one for the other would produce incorrect light output for that position.
The ANSI standardization of both units means they conform to a defined North American specification, which allows compatible replacements from multiple manufacturers as long as the correct H-series designation is matched.
The Tilt Cab body style designation appears consistently across all listed years, indicating that the H4651 and H4656 fitment data applies specifically to that cab configuration of the FRR.