My home was rewired and remodeled in 2014 but I am finding out that the electrician did not run a new thermostat wire from my upstairs thermostat. I have a newer-looking 4-conductor wire coming out of the wall upstairs, which goes up into the attic and downstairs into a wall. There are two old thermostat wires coming out of the wall in the basement - a 3 conductor and a 2 conductor wire. It appears the newer wire from upstairs was spliced to these two older wires somewhere along the way, but I don't have 4 live conductors in the basement. I connected a 9V battery to the conductors upstairs and tested them in the basement with a multimeter, and found I have only 3 live conductors down there. The black conductor in the thermostat wire upstairs either is not connected or something happened to the splice inside the wall.
I picked up a cheap wire tracer with the hopes that I could connect it to the black conductor and trace the wire in the wall until I no longer heard the tone, but it seems like I still get a weak tone because it is being picked up by the other wires. Is there any way to make this work the way I'm thinking? I can't think of any other ways to trace it.
Any ideas appreciated, thanks!