Thanks a lot for interesting reading Rich!
A little funny tho, that Ford made a "locking light" for Trucks with all-time 4x4.

 

I guess that full time 4wd and the "locking light" indicator are for "fancy" truck. lol

 

My guess is because your front driveline is always engaged so if you bump the handle or forget you left it in 4x4 you won't be happy when you get back on the road. Unlike the part time where you still had to get out and lock/unlock the hubs. Probably figured it was easier to forget with the full time rather the part time.

I compare it to current day 4x4 lights in trucks. Because now it's usually just a switch (sometimes still a floor shifter) so it's nice to have a light remind you if/when you're in 4x4

just my assumptions tho