Pos~
When / if you trace the "snipped" hydraulic line, it'll be interesting to see where it went in the cab.

 

It was just capped off. But the interior side end of it was bigger than the hole, so it was either enlarge the hole in the firewall and shove it through... or... I wasn't about to further damage the firewall so I snipped it.

 

Just a thought, but in the 'old days' trailer brake controllers actually were connected to the master cylinder and not electrical like they are today.