The auxiliary parking brake was called a "Mico Brake Lock" and it was used with hydraulic brakes. The valve in the picture just a trailer brake control that has been repurposed as a wheel lock while winching a load. If you use it that way, keep the engine running to keep the air pressure built up.
Jerry
Engine would need to be running anyway- winch is mechanical PTO driven. Old Garwood of a Duece.
Spartan
