The 4x4 lights in the dash get 12volts with key on, like most dash indicator or warning lights.
Then they are Grounded to turn them on, so shorted wire doesn't blow a fuse it just turns light on
I have never taken one apart but it looks like mechanical switches, SW1 and SW2 on circuit board
You should be able to check it all out with an OHM Meter
1993/4 4WD wiring diagram here:
http://www.therangerstation.com/forums/showthread.php?t=170637
You can see pins 1 to 8 on the switch in the lower left of diagram
Pin 1 is the common for the two switches
When you press the top button, 4high, you should see 0 ohms between, pins 1 and 2
Then high ohms or N/C when you press it again, switch OFF
Lower button, 4low, are pins 1 and 3 same test
On the Control module, lower connector, pins 4 and 5 activate the 4x4 lights by Grounding them, but..................
They are Grounded AFTER shift motor moves to correct position, they are not activated by pressing the buttons.
The 4x4 switch connecting pins 1 and 2, for example, tells controller to move shift motor to 4high position, which is set by the Contact Wheel in the shift motor housing
When motor has moved to correct position, controller then Grounds the Light bulbs, so never instant ON for the lights.
Controller will flash both lights if motor doesn't move, or contacts don't change, which is kinda the same thing
If pins 1 and 2 are disconnected, also 1 and 3, then controller moves shift motor to 2WD position and unGrounds all bulbs.
If all four 4WD lights are on then the 2 ground wires are shorted to ground, or the controller is bad, unplug controller's 5 pin connector and turn key on, if lights come on the wires are shorted to ground some where.
If lights stay off then controller was grounding them