We had an electrician do some wiring, including wiring two set of switches. The wiring could not be completed because the ceiling needed to be taken down. So he left enough wire to do the wiring later so that we could finish the walls. Now that the ceiling is down the electrician is not available. I could easily do this myself but I don't know which of the two wires goes to which switch as he didn't label them.

Besides hooking up a light and switch temporarily, is there some way to tell which wire goes to which switch?

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Connect an insulated wire in one of the cables to a hot wire, or, if the cables are already wired to switches, just make sure one switch is on and the other off, then test for voltage at the far end using a non-contact AC voltage detector (Walmart $6).


use an ohmmeter.

just short out one of the cables in the ceiling, then measure to find out which one is shorted at the switch end

also, some of the cables have a running footage printed on them.

just check the printing on the cable.

there may be a batch number or timestamp that is different between the two.

  • I would do that the other way. Measure the loose end, while turning the switches on and off. Feb 5 '18 at 0:13
  • @Harper, yes to that, if the switches are already installed (it is not clear if they are). ... i said to measure at the switches because it is safer to use a DVM while standing on the floor because you usually need 3 hands for that
    – jsotola
    Feb 5 '18 at 2:50

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