1989 4wd not engaging

. I am just now getting into 4x4s that dont have a straight front axle. Before I purchase a friends 1989 4x4 I would like to hear opinions on what might cause the 4wd not to engage. Some say a solinoid. I am not to sure. Just looking for a few simple things I can check. :banghead:

If the front driveline spins in 4 wheel drive, but there is no power to the front wheels, more than likely it is the 4x4 actuator. It is on the bottom passenger side of the front differential. I believe that year, the actuator was gas charged. In the past I bought an electric replacement for my 94 Pickup. It worked great, and I think I found it for around 80 bucks.