[77newell]

FWIW: On my 93 coach with an air distribution block in the same location, I have one black line that I believe goes to the dash "supply" gauge and one black line that does to the air horn valve. I also had one line going to the solenoid valve for the vacuum pump for the dash HVAC controls - I replaced this pump with an electrical one that looks identical to the black pump shown at the edge of your photo, the electrical pump works far better than the air powered one.