Key in 'On' position, 4wd select switch in 2wd--
Red VSV 12v, Blue VSV 0V
Key in 'On' position, 4wd select switch to 4wd--
Red VSV 0V, Blue VSV 12 V
Explains why the red VSV (disengage 4wd) is the one that fails, it's always on unless in 4WD.
An interesting note on the actuator design, the diaghragm is designed to be at rest (default) in the 4wd engaged position. As long as your vacuum lines are correct, if either VSV fails, you should end up in 4wd. Puts my fears of the vacuum system a little at ease.
And if you're switching vacuum lines to check actuator operation because you're stuck in 4wd, the 4wd selector needs to be in 4wd (should take it back to 2wd and indicator light should go off)...or...if you're just trying to get home in 2wd, take the line off the red VSV that goes to the actuator and plum it straight into the manifold, there's enough line there if you rearrange them.