I am aware of how the TRE works with just a simple resistor, but im a very curious about how the switchable tre work (like those from blueguages.com) I have an idea in my head about how it works but im unsure how the actual one works. im just guessing tho. If anyone could draw a picture it would be much help. All i have in front of me is the wiring diagram, and im trying to figure out how to make a switch for it.