low air break pressure warning devices.

Looks like it's either visual OR audible. The old trucks used to have a flag that dropped down in front of your face mounted at the top of the windshield. I think your truck would still give a light on your instrument cluster, that should still count.

 

Long as one or the other works you are fine

 

This is a repeat of someone quicker than I am. The light is required for the deaf driver. The alarm is required for the blind driver.
I never personally encountered a truck put out of service for a low air light, low air buzzer, yes.

 

I've driven a couple of those old trucks that had the flag that dropped down. When the air was gone it dropped down and on the flag it said "jump dummy".

 

If the truck was made after march 1st of 1975, the low air warning has to comply with FMVSS No. 571.121. That says this: S5.1.5Warning signal. A signal, other than a pressure gauge, that gives a continuous warning to a person in the normal driving position when the ignition is in the “on” (“run”) position and the air pressure in the service reservoir system is below 60 psi. The signal shall be either visible within the driver's forward field of view, or both audible and visible.

 

FMCSA likes to put must be in complance of FMVSS...(federal motor vehicle safety standard), then they don't put in what that standard says in the FMCSR book.

 

lolwut.... blind driver?