'92 KW T800 low air warning lamp and buzzer not working

Hi all. So, as said, the light and buzzer don't come on. But they do work. When I turn the key to ignition, the warning lights and buzzer in the overhead panel all do their self test and turn on for a couple seconds. The high water, low oil and buzzer will stay on, but the low air light won't stay on. I checked the switch box on that panel board and the switch for low air buzzer is on. I turned all the switches off except the low air and still nothing. I did find that the ground connection on the pressure switch on the firewall was bad. I got that fixed so there's continuity from the pressure switch to the plug that connects to that panel. So, where's my problem? Is it that circuit board? Is it as simple as a fuse? I can't find any labeled for it, unless it's grouped with something else?
Thanks!

 

Both pressure switches are easy enough to get at. I could try replacing one or both, but if the ground is fine on the switch then the switch should be fine? I only checked the ground connection on the primary switch so far though. I should check the secondary as well. As far as the test cycle, my brother was also thinking that they probably have a separate power source for running that. I'm going to try chasing more wires today and make sure the connections aren't all corroded.