On a Digital Dash car the Hobbs switches,yeah there's 2, are called Turbo Boost Indicator switches.
The case of that assembly must be secured to the fender with a clean ground as the two are grounding switches. One closes at 2.5psi. and the other at 10psi. They are each adjustable under plugs with a tiny screwdriver.
Clean the assembly removed from the vehicle and check the case to each wiring tab with an ohmmeter and 15psi. of compressor air into the hose assembly, both tabs should be open circuit with no air flowing, and shorted to the case with 15psi. air. When they ground to the fender, through the metal case, they light each of the two lamps on the dash. You can try grounding the metal socket of the connector, unplugged, with the key ON engine off and see if the bulbs light up in the dash, they should when a ground is placed on each contact.