No power goes through the switch. It is just resistors that tell the 4X4 module which mode you selected. Fuses - 13 in the under hood box, 5, 28 in the dash box.
Be sure to check that you are getting vacuum to the lines on the front steering knuckles when you select 4X4 a very common issue with Fords with the auto hubs is vacuum leaks that prevent the hubs from engaging. Not hard to test but can be a PIA to repair depending on where the leak is. If you are lucky it is just a bad hose.
Jack the vehicle up, place it on jack stands and block the wheels.
Disconnect both vacuum lines from the steering knuckles. Plug one line and install a vacuum gauge on the other. Start the engine and select 4X4 mode. Does the gauge jump up to engine vacuum? Yes > next test. No > repair leak or solenoid valve and retest.
Next test >
Connect the Right vacuum line to the knuckle. Start engine and select 4X4. Rotate the right tire forward/backwards while watching the axle shaft. The shaft should turn with the tire if the hub is engaging. If it does then disconnect the line, cap it and do the same test on the left side.
If both engage and operate properly then you need to check if the transfer case is shifting. But I would bet it is a bad hub or seal on one or both sides. Very common.
Monday, January 13th, 2020 AT 7:31 PM