Tao Tao atv will not shut off

[Lonnie Wrights]

I have a little Tao Tao atv that was given to a friend that seems to have had a rought lifr but I have everything working and running pretty good, the issue I have is when you want to turn it off nothing kills the engine. Not the key switch, kill button or the safety switch on the rear. What is the best way to trouble shoot the ground circuit to fix this problem cause I can find nothing visiably wrong.