I just received this toner. I had to trace a thermostat wire stuck in the wall. The instructions are clear enough. By connecting the red wire to the accessible end of the wire in the basement and the black wire to a good ground, I was able to easily trace all the way from the basement to where the wire was coiled in the wall. Precise location so I only had to drill a tiny hole in the drywall which was easy to plug with the new thermostat.