Low air warning

I’ve replaced sensors and jumped wires and I can’t find reason why my low air warning light or buzzer won’t go off. Has a new buzzer and that does work. Is there a way I can wire in new or external out of the dash cluster low air warning light or something?

thank you

2000 freightliner FL112

 

No warnings at all, even when at 0psi?

 

None

 

Does the buzzer/light come on when you turn on the ignition first thing before starting the engine?

 

used too but doesn’t anymore

 

Buzzer comes on but goes out once I start truck

 

dup

 

?