Hi Joe,

the switch in the manifold: I fixed a hose from the compressor to the thread of the switch and checked with gauche and voltmeter. 1.2 bar I think.

the valve on the firewall: blow in from the manifold side and check the way to the IP. Give 12 V to it and check whether the way to IP is shut and the valve is vented.
For a short test you can hear the click when giving 12 V.

Tom