Air leaking out of this connector even after replaced.

Hook up to a different trailer. What does it do?

 

Bad brake chamber on the trailer.

 

If I remember last I had this problem it was a broken spring in a chamber. And an air leak from transmission air servo line fitting.

 

Your description of the problem is not complete. What happens when you push in the red knob? What happens when you pull the jonny bar? Those are quick release valves. Which one leaks red or blue?

 

Replace the used valve with a new one. Sounds like a bad diaphragm.

I thought those are called tractor protection valves.?

 

Thing most people overlook when diagnosing air systems is a lot of valves tend to have their exhaust open to atmosphere when they aren't being used. A lot of times its an air system component upstream or downstream of the leaking part that has failed. It just leaks out the open exhaust port because its the easiest place for air to escape.