In the second picture you can see the smaller gray hose coming into the compressor from the coalescing filter. You might also notice the small piece of rubber hose I zip tied to the rod that runs from the radiator to the firewall. It vibrated on the compressor with the engine running.

The second picture also shows the manifold with some of the components in place. The brass fitting on the far right is a check valve. (I have moved the checkvalve since this pic was taken.) The open electrical device is the pressure switch. The off and on points of the switch are controlled by addjusting the spring tension. The electrical lead from the compressor gets connected to one of the contacts on the pressure switch. The other side of the electrical relay in there goes to your switch somewhere in your cab.