Originally Posted by Bluegrass 7

Well it's not that simple.
The switch signals a module called a GEM.
The Gem operates a transfer case motor that moves a shift control shaft and electrical connections to the first position.
This operates a vacuum solenoid on the fire wall to apply vacuum to the front axle actuator.
When these actions are complete the Gem lights the dash 4H lamp.
If the case motor does not operate it is a Fuse, the motor, or the GEM module.
The dash switch seldom ever goes faulty.
Good luck.