1999 Freightliner fl-112 low air warning buzzer

Probably in an aluminum block manifold behind a kick panel where a bunch of air hoses come in. It'll be a sensor with 2 wires attached.

Wait - "and light" ?

What's the issue? Light and buzzer stays on with adequate air pressure?

 

If it’s not there, it might be on the parking brake. There might be 2 that look the same. It’s normally closed. The other ones for brake tail lights. It’s normally open. If you can read the part#’s on the switches, Look for the one that starts with NC, not NO.

 

Ok now do a leak down test and let us know if it does come on when it goes under 60 psi.
80% of repairs is 60% diagnostic

 

I thank some of the switches on those are under the dash in front of the steering colum and hard to get to.
Two different switches should set the alarm off so I would check the alarm first. Was it integrated into dash panel at that time? If that is the deal and it is bad just buy an old school buzzer and wire it in.

 

Some where along the line a strip was put in the dash above the speedometer and tachometer. I thank it had all the warning lights, turn signal indicator and alarm built into it ( integrated ). My years and even trucks could be all mixed up?
Those dash units were fairly expensive and we would just wire in an old school buzzer if that was the only problem.
Had a similar issue with White GMC trucks going to SC for road test. Low air alarm would not sound unless the engine was running. Key on engine off they would fail the truck and no drivers test. We wired in an old school buzzer.
I could be all out of wack but if you post the last 6 of your vin someone maybe able to clear all that up.
Or a picture of your dash.