I an hoping to install a new thermostat that requires a C wire. I pulled off my old thermostat, an old round dial type, and it was of course only connected to four wires. The four wires are the only wires in their sheath, but there is another set of 3 wires that were just hanging loose in the wall. I'm guessing they won't help me connect my thermostat, but I'm curious what exactly they are?
They are very old wires with cloth sheathing. My guess is the house did not originally have air conditioning and they needed one more wire so they just pulled an entirely new cable. If you were really curious you would have to trace them out to either the attic or crawl space. I would bet the other end is dangling near your furnace if they didn’t move it when installing air conditioning.