1999 GMC 4X4 wont engage all lights lit.

I am looking for suggestions for 1999 gmc 2500 4x4 system. All lights illuminated, push button 4x4 wont engage cant see or hear issue with transfer case, no grinding, I cannot locate the electrodes on front axle to see if they are the issue. Basically all the ligts for auto 4x4. 2hi, 4hi and 4low and nuetral are all lit up and pushing them has no effect. Pulling the ATC fuse did nothing but cause the lights to not illuminate.