This is a proof of concept pull cord kill switch design. Similar to what is used on boats and jet skis. A limit switch is installed in the box. When the key is inserted, it closes the switch. When the key is pulled out, the switch is open. I originally designed this for my DIY self balancing scooter. This is a thing in progress and should not be used as a safety device. Use at your own risk!

You can see this part being used in this video. https://www.youtube.com/watch?v=mjSqjPOZ7Lk

This was designed in Google Sketchup. I have included both the .stl and .skp files.