ok im curious on this now. My truck has the manual locking hubs to put it into 4x4. and then the auto button to engage it. if the hubs are not locked in, will the switch put it in 4x4 mode or not, ...
I believe if the hubs are unlocked and you engage the 4wd, it will engage the transfer case to the 4wd gear ratios, but the front wheels won't be engaged. A lot of people do this when moving a heavy load especially backing up and want the lower gearing but don't need the traction of the front wheels.