My 1997 blazer parked it last night left it in 4wd low took off this morning shifted N then pushed button 2wd would not shift into 2wd or 4wd high tried several times backing up shift to N . the 20 amp minifuse is good, none of the lights work on the switch none of the relays are clicking nothing happening when any of the switch buttons are pushed i also took the switch apart and cleaned the contacts put it back same results. I need to get truck out of 2wd low thanks mike

also i notice the dash lights and floor shifter lights were out

 

I have a 2000 S10 Blazer and mine did something similar in December 2009. I would have it in 2WD while driving somewhere, but when I shut off the engine and stopped in somewhere, I would come back and find it stuck in 4Lo. It would even switch on it's own while I was stopped at a street light.. So I checked my vacuum hoses to make sure they weren't loose or didn't have any damage. And they were good. So I took the 4x4 module out from under my kick panel on the passenger side and tried cleaning some of the corrosion and it helped a little. But every now and again it would randomly get stuck in 4Lo. The mechanic I took it to thought it was the switch on the dash, even though I told them about the corrosion on the control module.. But they insisted it was the switch and they replaced that and it was still acting funny. But it turns out it was in fact the module under my kick panel because it was so corroded. I would've switched it out myself, but I'm not all that great with wiring.. I'm not 100% that's the same case for you..? Just thought I would share my story. Lol.

 

it was the license plate bulb replaced it all is fine go figure