Couldn't find this fix to the 4WD not working so it might be a rare issue but if you're looking for a solution here it is:

1995 chevy k1500 5.7tbi 4WD stopped working. I assumed it was the thermal actuator and replaced it, no change. Next I replaced the transfer case switch, no change. I was getting 12v at the actuator but no current as it was not activating. The fuse #24 was intact. I couldn't figure out what to do next as all the other posts said it was either the actuator or transfer case switch. I metered the fuse box and sure enough I discovered the fuse wasn't getting enough power which was odd.

The solution in this situation was to bypass that fuse holder altogether. I cut the brown wire that goes into fuse #24 and joined a new wire to it. Then I ran that wire to a fuse holder. Out of that fuse holder i ran a wire to power ( I found a wire under the steering column that put out 12v when the ignition was on and 0v when it was off and spliced into it.

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