I have a lift bus with a parking brake safety feature. To release the parking brake you press down on the brake pedal and then release the parking brake.
Problem is, the parking brake won't release when you push down on the brake pedal. There is an air solenoid on the fire wall that allows air to flow to the safety feature valves which are also on the fire wall (see pic below). The air solenoid has power to it and I manually grounded it and it works fine, for some reason it's not going to ground when you push the brake pedal. I've traced the ground wire to a harness connector that goes through the fire wall, and from there who knows where it goes.
I've replaced the air solenoid, replaced all the switches on the foot valve, replaced the ESC (supposedly it goes through the ESC according to International) and the problem remains. I've looked on ISIS for a schematic for this with no luck. This is the first time I've come across this. I'm hoping you seasoned vets can shed a little light on this subject. Thanks in advance.