Parking break ?

In my case, my truck was a bare cab and chassis and on dirt. Locked up immediately. It was actually kinda fun to do a sideways skid at 30 km/h after the initial shock as I expected it to stay somewhat straight.

 

My old R Model Mack has red, black and blue...

I pull the blue one when new guys are coming for a road test....show them "know it alls".....

 

When I was younger, I asked my driving instructor, otherwise known as dad, what the blue button was for. Instead of answering, he showed me by pumping the brakes until the brakes popped on, then he released them using the emergency air supply.

I learned using the hands on method.