TRX 300fw Starter issue

So I am working on my project ATV and now i am to the point where I am reinstalling the battery and body pieces.

Before this part the ATV sat in a shed for about 3 years, up until like a week ago.
My issue is as follows:

As soon as I add ANY power to the atv terminals (battery connections, positive to the top of starter, negative to engine casing under carb) the ATV instantly tries to auto-start using the electric starter. I thought the button may be corroded so i uninstalled and cleaned it, but no luck, So then I COMPLETELY unplugged the starter button and the ATV still automatically starts turning over.

All other lights and switches work as normal, but as soon as I give power via a battery or charger, it attempts to start.

Any ides?

ps: I did NOTHING to the electrical system, it is all stock.

Thnks.

Edit: Upon working on it today, i think that there is the possibility the electrical system was worked on incorrectly from the PO i got this from.
I added some pictures (sorry i have no flood work lights, i work in a shed with no electrisity using head lamps) of the electical system in the rear, and terminals on the starter and engine ground.

What do you guys think? I cant read a wireing diagram so i have no clue if it is still wired up "stock", but there were alot of wires that had odd spots burt and taped over, and strange connectors that do not look professionally done