| Diagram | Fig. 33 — HEADLAMP, WIRING HARNESS, SWITCHES AND TAIL LAMP · ref 7 |
| Subsystem | electrical |
| Listed in parts books | 1966–1970 |
Bulb (50/40W vertical dip pre-focus)
Lucas 50/40W pre-focus bayonet-base headlamp bulb (PN 446, also listed as 414) for BPF-type headlamp shells.
Part number 446 is the Lucas headlamp bulb used in the pre-focus BPF headlamp shell, rated 50/40W for the high and low beam filaments. It's the bulb that sits behind the reflector and lens on the front of the bike, and it shows up across a long run of electrical-equipment and headlamp figures in the parts books, including the TR6C, TR6R, and T120R headlamp assemblies.
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This is a bayonet-style pre-focus bulb, meaning it seats and aligns itself in the reflector without adjustment once it's clicked into place. The old alias BULB414 refers to the same physical bulb, so if your parts book or an older invoice lists 414 instead of 446, you're looking at the same item.
If you're not sure which bulb your headlamp shell takes, pull the old one and check the base and filament configuration before ordering, since headlamp bulbs across the British bike world share similar bases but not always the same wattage or focus.
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