Sounds like the security system. Lock and then unlock the doors with either remote or actual key then try again
Is the light flashing? Does it change when the key is turned to on? (Not start)
Yes flashing in the on position.
If you leave it in on position it goes away but truck still won't start. Just cycles the the dash readings
Ok, here is a video with more things to check. Still looking like a security system issue, just didn't reset a easy as mine did https://www.bing.com/videos/search? q=f350+dash+light+looks+like+car+with+lock+flashes+with+key+on+will+not+start&vi ew=detail&mid=CF56060118075F98B753CF56060118075F98B753&FORM=VIRE
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