Truck is a 2000 Blazer ZR2, 3 Button 4x4 set up.
Went to use the 4x4 the other day (first time in over a year) and of course it decided to say go eff off your stuck. 4x4 lights worked fine no blinking. So I got the truck home started to do some research. This is what I have found and done so far.
1. Checked and replaced the 4WD Actuator, Vacuum one under the battery. Old one was wrecked. Zorro attacked the rubbers.
2. Replaced the Vacuum Switch on the transfer case, was only a extra 16.00 and saw they also go out all the time. Good thing old one, the ball was stuck in the unit.
3. Ran a few new vac lines that looked ****ty.
4. Lifted the truck up, jumped in started it, put it in 4x4, and boo still no 4x4. Switch goes to the 4HI and 4LO w/out blinking. Looked under the truck the transfer case is locking the drive shaft to the front diff, making it spin as it should in 4x4.
5. At this point I pulled the battery while the truck was running to check to make sure the vac diaphragm was working and pulling the cable to the front diff., it is. So I shut off the truck got under it pulled the other side of that cable at the front diff to make sure it was attacked to the fork thing. It was. It also moves in and out at about 1/2" as it should.
Now I don't know where to start looking now.
What I can figure, Vacuum works as it should, Transfer case works as it should. So now the front hubs are not locking?
Meh. I did my best to tell you guys what I did so you know, thanks for the help!

 

Little update, checked the fuses there fine.

 

How well (smooth) does the cable move? 1/2" is on the short side for movement. Total movement should be closer to 3/4" for full engagement. If you disconnect the cable at the front diff, can you make the cable move over 1/2"? If not, replace the cable.

Next, with the passenger side front wheel off the ground & the transfer case locked in 4HI, manually try to engage the front axle while spinning the passenger front wheel. If it stops, then the front axle has engaged properly.

 

Well sorry for the delay, been busy. I got the truck up today. The cable moves freely. But the shaft on the front diff that cable goes into seems to only be moving closer to a 1/4 of a inch? The tire will not lock either. So is it something in the differential?