Sketchy 4wd...

I can only get my 4hi to engage if my truck is cold when i start it up. I'll switch the lever from 2hi to 4hi and shift into reverse. The 4wd light will usually click on within a couple minutes(on a good day), and everything will work perfect. when I get 4wd to engage I can usually switch it on and off as long as I don't leave it off more than a couple seconds. When I turn 4wd off and reach operating temperature I can't get it to engage again unless I turn 4wd on and leave it until it engages, which only sometimes works and takes forever. I've replaced all the vacuum lines, and cleaned a couple contacts, but I haven't been able to figure out what is causing this. Im really hoping that my actuator is fine, and I'm suspecting that its the switch that engages the actuator.



In this photo I'm wondering if this is the valve that switches the actuator on and off. 1995 DLX v6. If it is can I do a test with a multimeater?

There is a vaccum line that starts from the valve under the drives side front wheel well -> runs to this valve(photo) -> and then has 2 lines running down to the actuator on the front differential. And 1 line running to the engine.

 

BuMp! So I figured out that the part I am talking about is called the A.D.D Solenoid, hopefully a little spit shine will make this thing function properly...