2011 Prostar brake lights come on with low air pressure.

Ok this has me stumped. I have worked on this quite a bit and haven't figured it out. The truck is running and is ready to go down the road and everything is ok with the brake lights. When the truck loses air to say 80 psi the brake lights come on. When the truck is aired up again the lights go off again unless you apply them. I have chased the harness from front to back and it is good. I have replaced the brake light switch behind the gauge cluster and that didn't change anything. I unplugged all the switches behind the cluster and unplugged the body controller and the brake lights were still on. I unplugged the firewall connections and it went out so it is in the cab somewhere. Any thoughts before I take it to the dealer?

 

Laptop would be nice and I've looked at what to buy with a varied stable of trucks but haven't pulled the trigger. I've pretty much given up being able to find the issue myself. I will post what the issue was when it comes back. I have one in visiting to get the idle timer shut off so this will be a bit yet.

 

They updated the body controller thinking they had it. They were wrong. Today they put on a test body controller and programmed it to the truck and supposedly a new body controller is the answer. Two techs with a laptop and 8 hours.

 

That's where the brake lights would come on when the truck was shut off and sat for a couple hours.