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!

  • The high-tech solution would be to attach a time-domain reflectometer to the cable, which can tell you how far along the length of the cable the break — and splices, and any other irregularities — are, while the tone probe will tell you how that length runs in the walls. No idea what's practical for the DIYer, though, unless you happen to have a friend that works in communications? – Kevin Reid Jul 11 '20 at 14:15

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