William,
Per the diagram the red wires to the 2 light banks above the voltmeter each drive a single light. They each go thru a butt splice and then to connector C26. Thus I don't think a loose red wire is causing the the 2 banks to be inoperative. If you can get the # off the red wire, you can figure out where it is supposed to go from the diagram.
Check to see if there are any other white wires that are supposed to be connected to the voltmeter gnd terminal. The diagram indicates there should be at least 3; the ground supply, a ground wire to the fuel gauge, and a ground wire(s) to the light banks above the gauges.
As to the alarm, if you haven't already, start the coach and let it run until the air gets to operating PSI. If the alarm quits, it is probably OK.
Good Luck, Steve