Explanation of the Drawing : Green - Allen screws  Red - Springs Gray - steel balls that usually come inside ball bearings

One of the two inputs ( the bottom barb fittings ) will be controlled by a switch able solenoid that will allow air to pass throe or not with a flick of a switch . It should be the low boost setting , because that's the first one that will get activated when a set boost is reached . In other words , It will be blocked if you desire the high boost setting . If you want the low boost , that solenoid needs to be open .