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

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!