The toggle switch should get its air supply from a common dash manifold. At operating pressure (90 psi and above) you should hear a short exhaust of air when flipping the switch down, less than a second. The toggle switch supplies air to a pilot control valve located near the leveling valve. When air is supplied to the end port that the toggle connects to the suspension should exhaust out of the pilot valve exhaust port. This functions independant and after the fact of the leveling valve. The pilot valve is a round canister about 1.5" x 1.5" with a 4 bolt mounting flange. They are notorious for hanging up and plugging up, especially if it sat around. Make sure the exhaust port is clear and disconnect the lines and spray penetrating oil in the pilot valve ports.
Hans Remmers's post in Old Mack Keychain was marked as the answer