Anti-theft won’t let me start my bronco

Hello, are you talking about factory antitheft? Or are you talking about an added on aftermarket alarm device? If you are talking about factory anti-theft, it can be disabled by either turning the key in the door lock cylinder or in the ignition cylinder -- if the remote fob does not turn it off or work. Try the driver's door lock cylinder first. If it is an added on device, have it removed. Most are buggy and unnecessary and ineffective / unreliable at this point. Factory Anti-Theft systems are impossible to defeat. You have to repair the components of the system that could be faulty, such as door ajar switches, door lock switches, ignition switches, and so on.