Help please. I have a 1997 f150 4x4. I turned on the 4x4 and now it won't turn off. I have the switch. What can I do to fix it?

 

99.9% sure the transfer case motor is stuck operated.
In other words it did not return back to normal 2wd position.
To get the truck useful again until you find why, remove the motor and manually turn the shaft back to 2wd and the motor back to 2wd so the circuit board contacts release the front actuator. Put the motor back in place until you get to work on the issue.
I would say the case motor either stuck or power to reverse the motor is missing. You can test the operation with the motor down and see what it does.
Good luck.