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
Looking for a Used F-350 Super Duty in your area?
CarGurus has 1,224 nationwide F-350 Super Duty listings starting at $6,999.
Search Ford F-350 Super Duty Questions
Ford F-350 Super Duty Experts
Related Models For Sale
Used Cars For Sale