I have a 99 379 Pete, the low air warning won't shut off at 120 lbs. Is it located on the air dryer, or where is it?
Take off the plastic panels under the dash. The sensors are in a aluminum air block mounted on the floor just to the left of the steering column.
There are two aluminum blocks down there. They each have a low air sensor, one for the primary and another for the secondary. Look at the tags on the wiring.