I've been doing some reading, and it appears my understanding of Ford's SOTF 4x4 is correct, as of 2013. If I have no vacuum to LOCK my hubs, I will have to get out, turn my hub setting from auto, to lock, and 4x4 will work. It seems sometime around 2015 Ford changed to the opposite, using vacuum to maintain 2wd, and no vacuum moves to 4wd.
Here is a quote from FTE in 2013 "The auto hubs use the vacuum pump. If ever your vacuum pump dies or gets a leak in it. (which I've had happen several times over the years). You will not have any 4x4. By turning to Lock, You can have 4x even though the vacuum pump is lost."
If this is correct then the solenoid that OP is using, likely won't work for my truck.
Jerry