96 Mack CL700 Elite dump truck electrical and air issues

Greetings and salutations. I'm Marcus. I (usually) drive a 96 Mack CL700 Elite dump truck for a small gravel pit. The truck is old and beat up with lots of mechanical issues that we know how to fix. However there is an electrical issue connected to the air system that I'm not sure how to fix or even troubleshoot.

1st: When the Brake Air Pressure idiot light comes on, the brake lights come on (I'm not sure if this is what is supposed to happen, but that's the way it is.)

2nd: The idiot light used to come on at 90psi but now it comes on between 105 and 110. Which is a problem as it causes the brake lights to keep coming on when I have sufficient air.

3rd: The air compressor is super slow to air up and once it hits about 118 the dryer purges and the various air leaks slowly drain out the system and it doesn't start to refill until it drops to 90psi.

So, the more important issue (aside from fixing all the various little air leaks) is addressing the idiot light coming on too soon. I'm hoping to find out how it works, and more important how to get it to activate at the right air pressure.

Thank you in advance for any and all help that points me in the right direction,
Marcus

 

Thanks for the reply. I'll start tracing the lines coming off the compressor. I'm trying to think if there were any electrical wires in there. I think there was something on the air dryer, but I'll look around ... whenever I have the down time. Tis the season for everyone in our area to suddenly want rock. Like they just couldn't get their projects done in the summer. Oh no, gotta do it in the late fall just before the snows fly and while all the rain is coming down.
Maybe I can convince them to let me come in over the winter while we're down.

 

The air compressor was rebuilt a couple years ago and we replaced the entire air dryer unit last year. Any idea where that pressure switch might be? Perhaps under the dash on the firewall or behind the dash somewhere. If I have an idea where to look, when I get some downtime I can can tear into it. Sadly the outfit I work for is too small to afford anything even close to new. The Mack is the newest of our trucks and all of them has seen not only heavy use, but the owner of our company has put almost every truck we have on it's side at one time or another. We work in very challenging environments.