The Isuzu FSR 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 2002 with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Isuzu FSR Tilt Cab uses the H4651 sealed beam unit for high beam headlights across the 1996-2002 model years.
The low beam headlight position across the same 1996-2002 range is filled by the H4656 sealed beam unit, also specific to the Tilt Cab configuration.
Both the H4651 and H4656 are ANSI-standardized 4x6-inch rectangular sealed beam units rated at 12V, a format common in North American commercial vehicle lighting.
Sealed beam units of this type house the filament, reflector, and lens as a single fused assembly, meaning the entire unit is replaced rather than an internal bulb.
Although the H4651 and H4656 share the same physical 4x6-inch rectangular form factor and voltage rating, they are not interchangeable, as each is calibrated for a distinct beam pattern, high beam or low beam respectively.
The ANSI standardization of both units means equivalent sealed beams from other manufacturers conforming to the H4651 or H4656 specification are generally compatible, provided the beam designation matches exactly.
All specifications listed apply exclusively to the Tilt Cab body style of the FSR, indicating that other cab configurations, if they exist for this model, are governed by separate fitment data.