The "Service 4WD" light came on in my 01 GMC Sierra. I assumed it was the autotrac 4WD dash switch so I replaced it. Now the "Service 4wd" light is gone, but the new switch isn't working...the indicator light isn't lighting and the truck won't switch into 4wd or Auto mode. Maybe it wasn't the switch afterall....any suggestions???

 

either u have another bad switch ur fuse is blown or it's a transfer case encoder motor. encoder motors r bad about going out.