peterbilt air leak

They have a habit of going off at random. Mostly from leaking windshield.
The book says you have to have a visual or audible warning.

 

The buzzer on an 88 Pete is on the back side of the idiot light cluster in the dash. That maybe the pressure of switch that tells the buzzer to work. The law states your required to have a low air warning light and buzzer. I don't think it an and/or buzzer

 

That is a breakaway brake light switch for the trailer circuit. Kicks trailer brake lights on if the supply line is severed. All the older trucks had the 2 brake light switches. Most of the emergency trailer ones were removed over the years. I.e. the main one goes out so on the side of the road u pull the trailer one out. Plug the hole or switch it with the bad one to restore all service brake lights.

 

This is actually completely incorrect. As stated it's a low pressure air switch. Here is a picture from the book of that manifold.

 

Yes sir. Low pressure air switch that triggers the brake lights when air pressure drops in trailer circuit. If working correctly it should trigger lights and sirens if u rip the red glad hand off.

 

If that's the case, any time you set the trailer brakes it'd set your brake lights off lol.