A kill switch on the starter won't kill anything but cranking. It will not kill the engine, or disconnect the battery, or prevent push-starting, or prevent cranking with common jumper cables.
So before we can really give you any suggestions, you have to tell us exactly what you're trying to accomplish.
You should put ALL your truck's details & history (as much as you know) into
your signature(<-click that) so it shows with each post, as this page explains:
(click this text)
Phone apps don't always show signatures, so you may need to switch to a real browser in desktop mode on your phone, or just use a desktop/laptop computer. Put your location (nearest city) in your profile &/or signature, & upload an avatar of the truck. Not all its details are relevant to these issues, but you don't necessarily know which ones are relevant, so just put everything in now. The more pics you post (NOT in your sig) of the truck, engine, wiring, labels, & undercarriage, the more likely we can help you.