The vacuum line, on my 1987 Dodge W250, that operates the front axle disconnect is not hooked up. The engine is a 318. I have not found an obvious vacuum connection point on the back of the engine. Does it make a difference whether the vacuum line is connected to the intake manifold or the base of the carburetor?

 

Yes. You want manifold vacuum for the 4x4, the port on the carb might 'ported vacuum', which is the exact opposite of manifold vacuum.