If you can upload a picture of the setup, it might help. There are a lot of different types of cut off, etc...
Check to see if the red key shut off switch is connected to the battery, it may have been disconnected at the battery post. If it's connected and you suspect the shut off is at fault, remove the shut off portion or bypass it by connecting the two wires together. Or if you have some wire and splices to reconnect it all, just do that until you can get a new shut off, if that's the way you want to go.
I have a this type of shut off that kills the connection at the battery post itself. https://www.harborfreight.com/batter...tch-97853.html
Very simple function that physically removes the connection from the battery post.