Scott,
The low air pressure buzzer is behind the dash, probably near the center. The signal comes in on wire #553 and is split between the buzzer and the low air indicator. It is a white wire probably labeled Low Air. If the indicator works and the buzzer doesn't you probably have a bad buzzer. A broken wire is possible but not probable. If neither the buzzer or indicator work, I'd suspect a bad sensor at the air tank. Again, could be a bad wire/connection, but less probable. (Above info is based on an 03 Patriot diagram but should be the same).
Steve