Truck Repair: Low air pressure switch, kenworth w900, air sensor

Question
I have a 98 kenworth w900. The low air light lights up but it does not make any sound. I checked all the fuses, wires, and even replaced the unit it's self but it still won't make a sounds. Any direction you could point me in to fix this? Without buying an aftermarket alarm to wire to the light?

Answer
You replaced The low air sensor? After that about the only thing you can do is start tracing the wiring would start by seeing if you got power to the sensor if you do try bypassing the ground and run a temporary ground to something else that will at least tell you if you have a power problem or ground problem. or sensor is bad