Pacbrake air connection

[Algoma]

Finally got around to investigating why my pacbrake doesn't work. Had Allison check that the transmission is sending the correct signal and that was working OK. Ran some tests using a 12v battery directly on the pacbrake solenoid and discovered that once the air bags are fully inflated there is no air pressure to the solenoid. It appears that someone in the past has teed the pacbrake air line into the discharge line of the air dryer. Therefore there is only air pressure during the charge cycle and none during the purge cycle when the compressor cuts out. I am assuming the air line should be connected to the output side of the reservoir which feeds the level control valves for the air bags. Can anyone confirm this?
Mystified.