theft light blinks

My F150 has an issue starting, when I begin to turn it over, the overdrive light turns on and the theft light in the dashboard blinks rapidly and the engine will struggle to turn on, I've found a way to overcome it by continually clicking the ignition back and forth until the light no longer comes on which lets me know it will start then. Do you happen to know what could be causing this? I've checked my fuses and they all seem to be fine.