try to disconnect the bad speedo bulbs, one may be partially shorting out sending power to ground.
replace the connecting block near engine with a new one, or wire nuts. the old connecting block is ridiculous in design, and prone to getting alot of muck in it.
examine wiring throughout the bike looking for pinched, or damaged wires. check all connections inside the headlamp casing.
All of mobies use lower watt bulbs than that (6v-8w, 12v-16w aprox.) allthough if anything, that should be brighter. I might be concerned about it draining too much power.
I do not know about that diagram, but I removed a bad switch from my system. I simply looked at what connections where made with the switch in each position, and wire nutted together the wires to replicate the on position.