2000 Blazer 4WD issue

I'm having a problem with the 4wd on my blazer. Currenty when I press the auto or the 4hi from 2hi, sometimes it will change, and others it won't do anything when I press the button. I just went to the dealer to get the switches to replace. The parts guy told me that there was a switch on the transfer case and one by the fron t axle. I found the one on the front axle and changed it out, but still having the issue with changing from 2hi to 4hi. Sometime the light will just blink and go back to 2hi. The dash switch also if i get it to go into auto, then hit the 2hi button it tries to go into 4lo. Does this sound like the dash switch causing an issue? Also, does the switch on the transfer case exist? and where on the transfer case is it?

Thanks

Rick