Looked at the wiring diagrams this afternoon, and if you connect up the "common side" of the fuse block under the shelter (can be determined by pulling two fuses and then using an ohm meter to see which of the two fuse holders are connected together electrically....)
I am pretty sure it is the tops of all the fuses are common for the engine, headlight, horn and instruments.... the accessory and parking lights are on a different circuit from the key switch... the TL1, TL2 switch...
When you hook up the common side of the fuse block to the positive terminal of the battery, all the instrumentation lights, gauges, and headlight should all come on as if you turned the key on to start the bike... if you have a bad switch or wiring to the ignition switch, this will bypass all of it (except for the TL1, TL2 switch for the parking lights and accessories)
Good luck and let us know how you make out.....
Rich