1999 SCab 4x4, 5.4L. I was recently on a barbary sheep hunt in New Mexico on a ranch called the Bonney Canyon. Got my ram on Friday, so just piddled around the ranch on Saturday. It started raining early and I ended up spending the entire day in four wheel drive. I was about to climb up a particularly rocky and steep road and decided to put it in Low Range and just crawl up it, since it was very slick and steep. My Low Range would not engage. I put the truck in neutral, flipped the switch (Oh how I wish I had the lever!) and nothing happened. I didn't hear the usual knock and clunk that comes with Low Range engagement. So I drove around a little in 4Hi and still nothing. No dash light, no sounds, nothing! So I went ahead and crawled up the face in 4Hi, and just about at the top, we saw a herd of sheep so I shut the truck off and sat while we watched them through our binocs. Once they had left, I started the truck back up, and put it in gear, but the darn thing wouldn't even move! So I backed down a little ways, (all this time the shifter is still switched to 4Lo, but still only engaged in 4Hi) and when I put it back in drive, the big clunk came, 4Lo light came on, and I was in 4Lo. What gives? The underside was caked in a days worth of mud, but it was probably only 50 degrees F, not very cold.

 

on my 04 (not sure on your 99) have to put foot on brake, shift to neutral, change switch. try this next time. good luck