Anybody familiar with 800 Intruders?

1996 model, only electrical deviation from stock is a sealed battery.

Has power to the key switch, all the lights work. However, I seem to have no power to the fuel pump, horn or ignition switch.

To date have disassembled and cleaned the contacts in: key switch, kill switch, ignition button. No change.

No popped fuses. Supposedly there is a main breaker, but I can't find it...

The relay that hooks to the seat pan makes one click when the switch is turned to on. I can jump the solenoid terminals and get the engine to spin over, but not fire off.

All the fittings under the tank and seat are clean and tight, no corrosion, no loose terminals, no broken wires. Battery is at full charge and passes standard load test.

I'm lost.

Follow the power with a voltmeter. Power from battery - you said good.
Power to Kill switch - Good. Do you have power out of kill switch? What color wire...does that wire go to ignition switch? If you run a jumper wire from the battery to the ignition switch, does everything start working?

That helps you narrow down the problem location.

Decades of troubleshooting experience on equipment, the problems nealry always end up being a loose or bad connection.

A schematic helps, but without one, just start following wires and colors.