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So when I've got a '80 KZ750 LTD that isn't starting. What keeps happening is, I'll turn the key, and the headlight and neutral light will come on, But the second I press the ignition button, the whole thing dies and there's no power at all. Then no matter how I turn the key, it won't come back on, as if the battery is missing. This has happened a few times and I keep trying the key until a day or two later it turns on and the bike works again. I'll ride it for a few days and then the problem repeats. I'm thinking a lose wire or connection somewhere but I don't know anything about electrical so I have no Idea where to look. All I know is the battery is good so it's not that. Any Ideas would be welcome.

Check to ensure that the battery cables are tight and the connections clean at the battery and at the other ends of the cables. Ed

Have you tried jiggling the key? Anyway, although ignition switches do go bad, this sounds an awful lot like a bad battery. Sitting allows the voltage to recover somewhat. If you take the battery to an autozone or whatever they can test it for you.

the ignition switch on my 1980 750/4 E1 just plain wore out earlier this year. Bike randomly died and would restart after key jiggling or randomly would not start without key jiggles. I replaced it with one of these.
www.z1enterprises.com/ItemDetails.aspx?i...lock&item=EM40-80610

Very easy to do but be sure to check the warning in the link above before purchase.

Before you look at replacement switch check also for good connections at the battery and earth, the main fuse and there is a big connector in the headlight shell which connects to the ignition switch. The wiring diagram in your manual (check also the filebase here) will have a small diagram/table like the one below showing ignition switch connection (at the large connector in the headlight shell) and you will need a multimeter to check for continuity/resistance

Many times you can get rust or corrosion at the ground terminal, where the ground wire from the battery attaches to your frame or motor, follow the ground wire to where it's attached remove the bolt holding it, & clean the terminal & the area where it attached , to make sure you're getting a good ground
Pete

As long as you are going to be cleaning connections, it would be a good idea to go to Radio Shack or a local electrical parts store and get a can of Deoxit and some small brass brushes. It is a little pricey, but it is DA BOMB for cleaning electrical connectors.