2008 Peterbilt 389 with C-15 Cruise Control disangages and Engine Break doesn't work

First, the cruise control disengaged, and then work, then disengaged. Now, to the minimal move of the truck it will disengage. The engine brake now started to work intermittently. It also disengages itself.
I am not sure if it is related but, on the last trip, when I pressed the brake pedal, the dash lights came on.
I read many post (not specifically for my truck), and they mentioned I should check the clutch swith and brake switch, but I couldn't find them.

I appreciate any help I receive!!!

 

thanks GrapeApe, I will check it out in my 10 hour break.

 

I was able to find the problem thanks to you. the cable on the clutch switch was cut (I tried to upload a picture but I couldn't). Apparently, it was touching the frame, maybe doing a short, so even me stepping on the side step will disengage the cruise control. Thanks to you I was able to fix the truck myself and continue working which save me a lot of money. I appreciate very much your time and sharing your knowledge. A frustrating problem and a relatively easy fix.