Check the fuse box and starter switch, sidestand kill switch and clutch safety.

Also check connections at starter motor.

Also check the main fuse at the starter solenoid. Its on the left, down near the starter motor. At least on Post-Kats

What voltage reading do you get directly from the battery terminals with a voltmeter?

Check your wiring, clutch safety plugs in under the tank. and the relays at the battery box are plugged in. What year is the bike pre's have a circuit breaker at the battery box, post have a fuse. I'm guessing you un plugged something, or the ooops switch (run switch) was off. Possibly the clutch safety switch.

1999 Kat 600

I have some extra details:
Battery fine - 12.33V
No fuses blown
She is wrapped up like a black mummy, so no frayed wires that I can see, and I don't know where each wire goes since the are all taped up together.

I didn't see anything so put her back together. I fiddle around with the kill switch a bit, going on and off repeatedly, and finally got her to start, but inconsistent. This is peculiar, so maybe this will help diagnose the exact issue. With key turned, if I turn off the kill switch and the rpm's gauge blips up, then she'll start, if they don't, she won't start. Sometimes she will even blip up when I turn the kill switch on too. The engine isn't on, no throttle, just key turned and pressing the kill switch on and off, is that normal? Sometimes it will blip up as high as 3k rpm when I turn the kill switch off. At one point too, the main front lights weren't on, only the small reflector light was on, and she wouldn't start and the rpm wasn't blipping. Now the front lights are on and she seems to be consistently blipping the rpm gauge when I turn off the kill switch, and I can start her every time. What is the issue, or is there an issue, is that normal? All done on the centre stand too, so hard getting it on that thing, so until I know if I have an issue or not, going to leave it there.

With the kill switch ON it shouldn't start at all!

I'd say you have a grounding problem someplace, and it's grounding through the kill switch. Careful you don't melt the wires with starting current!!

Check all the connectors and recheck your grounds. Multimeter fun for you!!!

Sorry, had the on/off reversed, she starts with kill switch off, but only if the Tachometer blips up when I switch it to the off position. No blip, no start. Why is that, do all kat 600 do that? Or is there some wiring issue that is causing the Tachometer to blip up sometimes when I push the kill switch?

clean the switch, there is a post on setting the bike on the center stand correctly, If you find it hard, you're doing it incorrectly.

+1

Don't wrestle or force the bike onto the centrestand. Use it's own mass to your advantage.

Full weight on the footstand, you are pushing down and guiding the bike back over the pivot- physics takes care of the rest.