I have a 2003 Ranger XLT 4x4, with the rotary dial 4x4 switch on the dash. It doesn't get driven all that much, just under 70k miles. Last winter I used it in the snow and noticed that when driving around in 4-high it would occasionally just come out of 4x4, light on dash would go out. If you'd turn it back to 2wd and back on to 4-high a few times it would work again for awhile, but then just turn off again. Theres no flashing 4x4 light or anything, just seemed kinda random. Otherwise everything was normal.

I would like to get some ideas of what to diagnose before this winter. I was thinking maybe the shift motor may have some dirty contacts due to lack of use??

It is very well maintained and quite clean underneath, no rust problems or excessive corrosion on anything.

Thanks for some ideas!

 

The 4WD module(TCCM) sends voltage to the 4WD switch when key is on.
In the 4WD switch are 3 resistors, one for each setting, OFF, 4hi, 4Low.
The voltage the 4WD module gets back from the switch, after it passes thru the 1 resistor, tells it what the switch position is.

This is similar to cruise control controls, each button uses a different resistor so cruise control "brain" can tell what button was pushed by the voltage change.

Google: 2003 Ranger Transfer Case Control Module

If the 4hi actually changes back to 2WD then problem could be in the switch or the 4WD module, misreading voltage from 4WD switch.
If the light goes out then motor has to be moving to disconnect it.
The 4WD lights are simple contacts in the motor housing, when motor moves the 4 contact "switches" located on a wheel in the motor housing open and close, this tells the 4WD module when the motor is in position for 2WD, 4hi, 4low, and these contacts also power the 4WD dash lights.

Flashing light means motor didn't respond to 4WD module, or didn't move far enough, which is often just a fuse issue.

Here is diagram for '01 Ranger 4WD system, its the same as '03, fuse #'s may be different, but I don't think that is your issue.

 

Wow, very helpful info. Thanks a bunch RonD! I'll go check some stuff.