I have a panel in a closet with my phone (RJ11?)cables in there. enter image description here

I want to convert one of those to RJ45. I want the cable that goes into my living room. I know there are connectivity testers out there, but those work with cables that are already terminated in RJ11 or RJ45. How do I figure out which one of the blue cables I want to change?

  • I'm not seeing any "phone" (i.e. RJ11) connectors in the photo. Those appear to be RJ45 connectors, which are NOT usually used for POTS lines but rather are already network connectors. The cables appear to be CAT5 although I cannot read the marking from the photo.
    – jwh20
    Feb 9, 2020 at 11:37
  • 2
    There are, however, a bunch of the cables with only the white/blue pair pulled out, which is typical of CAT5 used for POTS service. There's just the two RJ45's plugged together for actual connectors. The "(RJ11?)" is a reflection of the questioner finding that RJ11 is associated with POTS but not being too sure what they are looking at.
    – Ecnerwal
    Feb 9, 2020 at 15:46

1 Answer 1


Go to the living room and put a 9v battery on one of the pairs of wires. Then with a voltmeter, go through the cables in that closet one by one until you find the one that measures 9v across that pair of wires.

  • 2
    ...and then, for all that's good in the world, LABEL IT!!!
    – Ecnerwal
    Feb 9, 2020 at 15:48
  • this works well unless those wires are shorted. use a DMM to test first.
    – dandavis
    Feb 9, 2020 at 20:50

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