Was wanting to use my R model Mack to supply air pressure out in the yard and cannot get the emergency line to supply air for an impact wrench. Never has done this in the past. I'm assuming this tractor protection valve has frozen it's piston in the bore from non use as I've not pulled a trailer with the truck in many years. For what I'm doing with a need for air, I usually use my old B-61 Mack and it's TP-1 valve works great, but it's used fairly often. Thinking I changed that TP-3 valve back in the late 1990's due to leakage or wouldn't stop bleeding air but I've slept since then.....
Ive seen numerous quick connects plumbed straight into an air tank. I must not be understanding what you are trying to accomplish.
I usually use the emergency line normally feeding a trailer to supply external air. Basically the same as many truckers do with a tire air chuck. I have a couple trucks with couplers plumbed into an air tank, but this truck does not.
My dumb ass. It works as it should. This truck, (1980) has the three button controls. You have to mash the black one, then the blue one to release the tractor brakes. When you mash the black button air flows from the tank into the system. With the black button pushed and the red button pushed, air readily flows from the TP-3 valve as it should. This is where I connect my gladhand and air line carried in the truck.
"push to charge trailer while parked" 3 valve/button