Hurry!  Before beer thirty starts, see if you can get the seat and toolbox cover off.  Then you can sit and stare at it for a couple cool ones

Assuming that you don't have some catastrophic harness failure, I imagine it's pretty simple.  You're gonna have to start at the fuses and the positive supply end.  Since the taillight comes on, it's not the negative side.

The Red/black is the + supply to the ignition switch.  The Orange is the supply for the headlight etc.  Green goes to the handlebar switches.  The Brown is the "taillight only" supply that works in On and Park.  If you want to check the switch with a meter or test light, see if you have 12V between the Orange and Ground with the switch turned On.

Like Justin, I don't suspect the switch, but it's a good place to start.  

BTW - if you don't have the main supply power, you won't have any control for the starter relay.  Don't bother worrying about that.  It ain't there

A longshot but - does your key have a heavy fob on it?

A buddy of mine had one his kids gave him - bouncing in the wind it managed to destroy the inside of the ignition switch. The bike was purring , we stopped for gas he went to start - we could get a tail light but nothing else - totally dead
The bouncing of the fob over a 6 month period had smashed the interior connections of the switch.

It is a long shot but better check the ignition switch

Taz is fixed and it was easier than I thought...
I assumed and it bit me in the ass.
All it was was a faulty battery; A new one put Taz back on the road.
My corner mechanic is a great guy. Did me right.
I charged the battery and assumed it was charged having no voltmeter or good charger with an indicator.
My bad for being so dumb and tool-less.

Bottom line: Taz is a great bike, no real problems in the 2 years of ownership. 1 weak battery is it, can't complain about that.
I'd recomend an S40 to anyone; But beware they become part of the family...

TC, what is a Neon style battery checker? My old load checker suffered a fatal meltdown, Milton fried. I havent replaced it yet. Harbor Freight has a few low buck options, but if there is a cheaper approach that will tell me the story on whether or not a battery is okay or not, I will go that way. Volt meters just don't tell the story. I guess it does IF you can hook the meter up & hit the starter & see how far the voltage drops. Okay on a bike, tough on a car.