Thot I got a good deal! 97, 4.6, 4x4 Lariat supercab. I discovered the blue vacuum line coming from the terminal on the passenger side firewall was cut in two. I spliced it together with a piece of rubber tubing. I have discovered that the 4x4 light comes on but it doesn't shift into 4x4. When I put it into low range it gears down but once again only rear wheels. I bot a manual but it hasnt arrived yet! Need some recommendations about where to look, or what to listen for or where to look. Can I asume the inboard terminal is the low range switch and the outboard is the 4X4 switch? tanks

 

I don't know if a 97 is different than an 02 but the vacuum actuator is signaled to operate the front drive by operating either one vacuum valve or an other to make it operate or release the coupler.
With either 4H or 4L the actuator would need to operate then release when in 2wd.
Have some one do the 4H and see if it operates. It's out were you can see/hear it in the top front area of the axle housing.

 

Hook a vacuum pump up to the shift fork on the front diff. If it actuates in both directions it is working and it is the solenoid by the passenger fender that is acting up.