air brake question

So I am a bit new to all of this:
Yellow is Tractor
Red is Trailer.
When u pull out the yellow both yellow and red pop out and that is used for parking. In is for driving.
When performing the tug test and you have either the red in or yellow in which brakes are you testing?

 

I know two different brake eras, prior to about '77 would be the 1-2-3 system and trailers did not have springs. So it will run away when you tried to hook without setting it's brake. And the current two button era. Which is also useful.

Don't stress about the air brakes. The thinking and heavy lifting has been done generations before you existed. Just remember how to leak test and so on.

Sometime in your future if you have a defective truck or trailer with a bad leak, it will be up to you to come up with a safe fix to get stopped.

 

When you first hook up. Tug test to check that the fifth wheel is holding. Yellow pushed in (truck brakes released), try to go ahead gently, trailer should hold you back.
Or if you’re already all hooked. Both pushed in (all brakes released), move ahead a bit, maybe five mph. And pull down hard on the trailer hand brake (trolly valve) assuming it has one. Use to be standard on trucks, apparently an option now with some fleets.

 

September of 79, all trailers had to be equipped with maxies, except for some exemptions.
Now the reason that the red (trailer) valve is not to be used for parking, is, if you only pull the trailer valve and unhook,your tractor can just leave you standing there, thinking I sure messed up. lol