enroutemexicali

There are two air lines.

I think one is for the spring brakes. Air pressure compresses the springs, turning the brakes off. If the trailer disconnected from the tractor, the hose would sever. A set of springs would clamp the trailer brakes "on." This is a safety feature preventing the trailer from continuing on its way down the road.

The other hose is the service brake. There's no air pressure in it when you're at cruise. When you press the brake pedal, the pressure varies depending on how hard you press. Higher pressure makes the brake apply "harder." The big handle on the right side of the cab interior (you see it in the cab photos) is the trailer brake valve. It allows the driver to apply the trailer brake only, if desired.

The circular thing is the trailer lighting electrical connector.

I believe trailer regulations would allow 45-foot, 40-foot, or shorter trailers in 1973. That includes the dry goods van trailers owned by Rohr. Comments or ideas are welcomed. Your tags are welcomed.

Everybody must pay. It's not simple. Everybody must comply with regulations and export licenses.

This looks like U.S. or Mexico Customs. Possibly a bonded customs agent facility? That might be what this sign refers to: [https://www.flickr.com/photos/sdasmarchives/55218353012/]

Raising or lowering the landing gear.