Let me begin by saying that your site is the most informative that I found by far when I was trying to fix the 4WD on my 99 S-10. My situation was that when I pushed the 4HI button the light came on but no 4WD. With information from your site I replaced the vacuum switch on the transfer case, which was bad, almost fell apart when removed and still no 4WD! Then replaced the vacuum actuator which had a hole in the bladder and all is now well right? Wrong! Pushed the 4HI button and fuses blew, the dash went haywire and still no 4WD! The 4WD activation light switch was a dead short! I disconnected it and replaced the fuses and voila, 4WD! WooHoo! I replaced the actual switch a few days later when it had warmed up a bit and everything works fine now. Also found that the exhaust can burn holes in the vacuum lines. Fixed two of those and secured the lines away from the heat. The way I found it was that I didn't touch anything electrical and that's the only electrical part that pulling the 4WD cable can activate. I now have one of each part in my truck with some vacuum line and splices just in case and I would recommend this to any S-10 4WD owner! It may not be practical to change out in a ditch in the cold but it beats getting stuck or getting in an accident. I laid in the snow for three days working on mine but after you do it once it's really pretty easy. I sincerely thank you for the help that your site provided and hope that my info can help someone as well.
PS: I took my TCCM apart and to my amazement it was pristine on the inside! I at least had a bit of good luck. Thanks again, JM.