Forget the fork-mount Headlight
Go to the auto parts store & buy a pair of inexpensive 55w rectangular off-road lamps (mine were $20, silver box, @ Pep Boys). Buy an in-line fuse holder, box of fuses, some extra wire & quick-disconnect connectors while there, the latter compatable with your headlamp socket; if in doubt, take the lens set with you.
Mount the lamp to visor (it comes with a bracket). Two strands, ~5' of wire/ea., install connectors on end to plug into stock head lamp socket. Install fuse on one wire. Tape wires together at 8" intervals, then to the back side of helmet, & drape the rest behind you then loop it around on your lap - connect to the wiring harness into the head lamp socket.
The advantage of this system is being able to point the lamp *where* you are looking, not off in the distance or in the air when going over terrain @ night.
I used this setup @ our last enduro, duing the 9pm poker run. Worked just fine (tho no high-speed Baja setup), & learned more than once NOT to look at card doler & other innocent spectators - can you say blinding?