My new house is wired with CAT5 but hooked to telephone jacks in all the rooms. So I'm going around and wiring them up with RJ45 outlets.

I did 3 rooms so far and all is good with them. I just got to the master bedroom and the tester says miswire with 1-2 and 3-6 but I'm looking at both sides that I've put plugs on and they are both 100% wires correct.

Any idea what is the matter with my cable?

  • 2
    Are you sure there aren't other junctions where things could be miswired between where you're measuring the incorrect wiring?
    – Milwrdfan
    Commented Nov 24, 2023 at 20:23
  • 1
    Pictures of the wires and jacks? Commented Nov 24, 2023 at 20:29
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    If only 1-2 and 3-6 is swapped, that's not a problem. That's a crossover cable, and all modern ethernet equipment (post 2000) supports auto-mdix.
    – vidarlo
    Commented Nov 24, 2023 at 23:08
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    Are you by any chance following a set of instructions that says to use 568A for one side and 568B for the other? Your simple tester wants both ends of the cable to be wired exactly the same, either A or B but not both. In practice, the distinction has been obsolete for many years, and your devices will be perfectly happy with either type of cable (straight-through, or 12/36 crossed over). But pay attention to Gil's answer -- if your wires really are identical on both ends, the tester is telling you that something sketchy is happening inside the wall where you can't see. Commented Nov 25, 2023 at 0:02
  • How is the wiring laid out physically, i.e. does every cable run from a single location to a different room, or do the cables run from room to room? Telephone wiring can be arranged either way, but network wiring has to arranged with separate cables running from a central location where the switch is located, to each room.
    – Mark
    Commented Nov 25, 2023 at 0:24

1 Answer 1


There is a potential disaster when switching from phone circuits to Ethernet. Ethernet is point to point. That indicates that it has to have a continuous wire from the switch/router to the computer, no other stops on the way. With a cross over cable you can go from computer to computer but again nothing in between. Each computer is wired back to the switch/router, not from computer to computer.

Phone wiring is different that it can go from jack (phone) to jack (phone) without going back to the home point.

You indicate that the ends are correctly wired but the tester is saying they are not, believe the tester and look for a point where the wire was spliced,patched, ..etc.

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