2003 peterbilt 387 low air sensor location

truck is building up pressure just fine but sometimes all of a sudden air pressure will drop to zero and buzzer will go off and keep going for a few minutes. I know hta on our w9s and 379s the low pressure sensor is one the drivers side by the pedals but i've never explored this 387 but i'm guessing that its gonna be a sensor down under the truck by the tanks that sends signal to the computer by the glovebox that feeds the gauges