No power at the headlight fuse means a problem with the ignition switch or harness. The online diagrams are generally useless because the resolution is poor and much of them are unreadable, if someone with a Honda shop manual would take a high resolution scan it could be cleaned up and compressed quite a bit (once you get the contrast adjusted so the white space is truly white instead of shades of gray, the compressed picture file gets about 80% smaller) and that would be great. I can do a 400F drawing but we would need all the models and versions... the 750 as the longest production run with various models would be the hardest to get complete.
Anyway the power distribution is fairly simple: red wire from the MAIN fuse goes to the ignition switch. When ON, power is sent to the kill switch and coils for the ignition system, plus instrument lights, oil and neutral lights and brake light. This power also feeds the HEAD fuse directly, from this fuse power goes to the headlight switch. The tail light circuit is more complex, because of the parking light circuit... but again in ON the TAIL fuse is powered from the ignition switch. In PARK, the tail light is powered through the MAIN fuse only, using an extra contact in the ignition switch.
Haynes and Clymer books have "simplified" wiring diagrams that make troubleshooting much more difficult if you have a problem with stuff that was simplified out of the drawing... like the parking light stuff. The Honda diagram in the shop manual (also in the user's book but ridiculously small) is complete and shows every wire and component.