Four wheel drive

I have a dodge 1985 350 royal i ton. The four wheel drive is not engaging. I have checked the lines on the t box, one was plugged. Im not sure if this is what this is called “actuator?”. I put a main vacuumline to it and it did not engage. Dose that normally go out.

vacuum,on an 85?

its all mechanical.(whats not engaging,case or axles)alot of old dodges were full time 4 wheel drive)

whats a royal?

metoo.