4wd noy working..
 

I cant get my 4wd to do anything.. the switch on the dash flashes once when I start the truck but then dont come back on..my mechanic told me its the actuator on the front diff. But I dont know how to test ot.. can someone point me in the right direction on how to test it..

This is the initial video that helped me diagnose my problem
I had to replace the vacuum lines, the 4wd actuator was fine and on my 1999 blazer it sits under the battery tray and you can test it to make sure it works before replacing it, there is a YT video out there that shows you how to do it, I cant remember if this video shows it or not, I'm at work and cant watch it but I can look for it tonight.

When I pressed the 4wd button, it flashed and then went off as well. Since replacing these parts the 4wd has worked perfectly.

I initially found out the hard way that I had no 4wd, I went off road and got stuck in the river. I put it in 4 high and low and the front tires never spun, had to be towed out by a fellow Jeep owner riding in the river bed as well.

I forget the name but this is what I replaced, it sits on top of the transmission, its not hard to reach either. There is I think a ball bearing on one side, the one I had I was not able to push down, but the new one I bought I was able too. This part just screws in. I'm sure someone on here can name the part when they see this.

I cant even press the 4wd button.. the lights only come on for a secomd when tbe truck is started then go off and stay off..

Before I replaced those parts I checked the fuses and someone on here mentioned that the button assembly/selector switch may need to be replaced, but before I did that I replaced the others. Now I don't have to replace the selector switch.

Checked fuses..all were good

How do I test to see if my 4wd switch on the dash is working or not??

bump.. need to get my 4wd fixed before snow comes

I would start by checking all your vacuum lines. Mine did the same as yours light never coming on, I replaced all the vacuum lines I could see in the engine compartment whether they were related to the issue or not. You can by a 50ft roll of vacuum tubing on amazon for around $10. My vacuum actuator under the battery was doing nothing at all until after I replaced the vacuum lines. And almost ALL of my lines were rotted out.

If you push the 4hi or 4lo button does the transfer case do anything? regardless of lights you can still push the button. Just make sure you are in neutral when you do it.

I checked all the vacuum lines all are good.. I get vacuum up until the actuator on the firewall..but nothing happens at all when I press any button on the dash.

I am havin the same problem. I replaced a bunch of lines. the accuator. And still nlthin. Cables are good. Have olenty of vacuum. I have no idea what the hell is wrong. Confusin the hell outta meh. Grrr.