I have a 1990 B2600i 4x4 with a 5sp manual, I’ve had it for about 2 months. I thought that 4x4 was working because when I put it in 4Lo it seemed like it was crawling like it should.
Well last night we got a snow storm, and I got stuck and 4x4 was absolutely NOT working, but in 4L the gear range still changed but only the rear tires were spinning.

Later that night I started messing with it more, I pressed the RFW button probably 50 times, and slammed it into 4L and the lock light came on, but no 4x4 light. 4x4 does seem to be working now, I couldn’t get the rear end to spin like the previous night and I drove around in the snow for about 10min, however still no 4x4 light.
I’m afraid to unlock the hubs now that I got them locked and 4x4 supposedly engaged.
I’m not really sure what to do, I don’t have the mechanical expertise for that sort of stuff. It pretty much ends at changing spark plugs and oil.
I bought this for my 60mile commute to work in north Idaho over 4th of july pass. 4x4 is an absolute necessity for me.

 

I have a dumb response, but you said the truck is new-to-you. Go underneath and make sure that the drive shaft for the front wheels has not been removed.

 

I had the whole front end (really the entire suspension) gone through at a shop. I had a new rear end installed, and the wheel bearings in the front.
I'm thinking it is something electrical, or vacuum related to the RFW?

 

Are the RFW hubs vacuum operated? Common problem for vacuum leaks & faulty solenoids.

 

Yes they’re apparently vacuum operated. I will have to check for leaks when I finally get to my days off (working a 4 day 12 hour week this week).

I like the idea of the automatic hubs but I feel like a manual hub setup would’ve been more reliable...