That is nicknamed the "spider" harness. It supplies the ground to the Instrument Panel. Another good tip is to get some Di-Electric grease and put a little dab inside the connectors. It makes it MUCH easier to get them apart later on down the road.
The low air buzzer not working... You have a late model USAF truck, it has the brake warning light in the dash also. There is no known schematic for the split brakes system electrical harness, part # 5934093, NSN 2590-01-259-0285. Once you get all your dash guages plugged back in, you will have 2 "extra" wires, one male, one female left over. (These wires wont be listed in the schematic diagram in the TM, or the Peter Bog.) These 2 wires that "come from the left side of the dash, they are taped together, and the wire bands are # 127 and #167. These wires plug into the red BRAKE warning light in the center of the instrument panel, #67 and #27. This is one exception to the "dont plug in mismatched wire numbers" rule but for this harness is is OK.
If that doesnt fix the problem, you'll need to do some old fashioned troublshooting for the circut.
Check this thread, the 2nd post down for the info on the dual circut brakes. Print it out and keep it with your truck.
http://www.steelsoldiers.com/deuce/46951-dual-circuit-brakes.html
