My house is wired for ethernet, with the network closet on the 3rd floor (NC). The ethernet in all the rooms work, except for the connection in my office on the 1st floor. If I plug a laptop into it, it doesn't get any internet. Also, when I use a basic network cable tester between Room A and the NC, LEDs 2, 3 and 4 don't light up (the rest do, and do so in order). LEDs 2,3 and 4 don't light up even when just the master tester is connected to one end, if that matters.

Some background: when I had internet installed, the technician used a network tracer to identify the other end of the office's ethernet cable in the NC. Oddly, it was connected to a Leviton telephone board (it was the only one). He ripped it off, and crimped a connector onto it. When it wasn't working, I noticed that he had wired it using T-568B instead of T-568A like the other cables in the NC. So I redid it, but it still doesn't work.

Network Closet: enter image description here

Any ideas what could be wrong?

  • Could it be because I crimped it badly?
  • Is it an issue with the wiring?

Update #1:

  • I've verified that the tester works on a known good cable.
  • I'm crimping male connectors onto the cable (this is the cable coming out of wall in the NC).

Update #2:

  • I did some more research, and I actually have a Leviton telephone board, not a patch panel.
  • I unscrewed the wall panel in my office (the other end of the cable), and it turns out the builder used a Cat6 cable (blue) for the telephone jack, and a Cat5e cable (white) for the ethernet jack. This seems incredibly backwards, but it explains why the office's cable was a white Cat5e cable instead of the blue Cat6 cable used by every other room.
  • If the white cable is in fact damaged, maybe I can just try swapping the blue and white cables in my office and hope the blue cable is fine?
  • 5
    it's a break in the cable ... suspect the connectors first
    – jsotola
    Sep 28, 2022 at 18:58
  • 9
    Could it be because I crimped it badly? -- Yes. first place to check
    – Traveler
    Sep 28, 2022 at 19:20
  • 6
    Oddly, it was connected to the patch panel (it was the only one). He ripped it off, and crimped a connector onto it. So, "Oddly" was the other ones NOT being connected to the patch panel, and your network guy was an idjiot. Punched down to a patch panel is How It's Done Right!
    – Ecnerwal
    Sep 28, 2022 at 23:20
  • 3
    A was a standard that was just never widely adopted. idk why but B rapidly became de-facto standard. It's safe to say "No-one wires in A".
    – Tetsujin
    Sep 29, 2022 at 16:51
  • 3
    Is it the blue/white pair that works? I wonder if it was previously used for an analogue phone line and somewhere all three other pairs have been snipped. Blue/white is the default colour for PAIR #1 to a telco tech.
    – Criggie
    Sep 29, 2022 at 23:24

6 Answers 6


Don't crimp male connectors (plugs) onto the end of permanently installed ethernet cables. Ever. It is easier and much more reliable to punch down cables onto jacks, either individual jacks or a patch panel.

Even if you are not going to secure a cable to a surface, a jack and a short factory made patch cable is more reliable than a typical crimped plug. If I am installing a jack "loose" then I'd wrap it up with electrical tape to protect it and it will be fine for years.

  • Cables are extremely reliable unless subjected to real abuse (under a rolling office chair, rodents, pinched in a doorway, etc.)
  • Jacks are very reliable if punched properly and protected from damage.
  • Plugs are not very reliable on factory made cables. They are even less reliable when hand made. Factory made patch cables are inexpensive, so you replace them when a plug breaks or a cable gets pinched, etc.
  • 11
    This, a thousand times this.
    – Ecnerwal
    Sep 28, 2022 at 23:22
  • 5
    In more detail: crimping onto solid-core Ethernet cable needs a specific special sort of RJ45 plug and often also a special tool that exerts more pressure than a simple hand tool is capable of. Professional installers can get this right. Otherwise, just don't try!
    – nigel222
    Sep 29, 2022 at 11:52
  • 3
    Agree. And i like to add: When you can't avoid having to crimp RJ45 connectors make sure you have the right plugs. Cable can be stranded or non-stranded and have thickness varying anywhere from 20 AWG to 26 AWG. You have to have compatible crimp-connectors for the cable type or you will have bad contacts. And avoid CCA (copper clad aluminum) cables with crimp connectors. They will form rust on the crimp-contacts (redox reaction between Al and Cu). Also happens with jacks, but usually causes no issue because the contact area is larger.
    – Tonny
    Sep 29, 2022 at 13:17
  • 6
    This. Yes. I've been crimping plugs professionally for 30 years & I still can't get 100% working first time. A newbie has no chance. Buy ready-made patch cables, use a proper metal spring-loaded punch-down tool with cutter for the backs of sockets. These are 100 times easier to get right than plugs.
    – Tetsujin
    Sep 29, 2022 at 16:55
  • 1
    Some friends of mine once did a lot of hand crimping. They bought three crimpers, so three people could crimp at once. There were lots of failed cables — careful analysis eventually revealed a 33% failure rate. And then there was some fingerpointing, culminating in a sheepish "Three clicks? I thought I was only supposed to squeeze it to two clicks!" from one of the installers. Sep 30, 2022 at 23:37

T-568A vs T-568B doesn’t matter, as long as both ends use the same termination. They just switch a couple of pairs.

If lights aren’t flashing on your tester, then you have open connections. Probably bad crimping, as you suggested. Try recrimping the connector. If you end up with the lights flashing in the wrong order, you probably have mis-matched termination.

  • I forgot to mention that LEDs 2,3 and 4 don't flash even with just the master connected. Does that change anything (i.e., make it more likely to be a cable issue rather than a crimp issue)? Sep 28, 2022 at 19:38
  • 1
    @red.october If I recall correctly, my tester won't light up on either end if the wires are shorted, and only lights up on the master end if there's an open circuit. Do you have a multimeter or ohmeter? I would remove the the connectors at both ends and check for continuity between each pair of wires. There should be none. Then twist all the wires together at one end and check for continuity between each pair from the other end - they should all show continuity. If both tests pass, then the cable should be good, so put new connectors on each end and try again with your tester.
    – Mark
    Sep 28, 2022 at 21:38
  • @Mark, I'm not sure what you mean by "pair of wires". Do you mean each coloured pair on the same end (e.g., orange and white-orange)? Or do you mean the two ends of the same wire (e.g., the orange wire in my office ethernet jack and the orange wire in the NC cable)? If I understand correctly, your 1st test is to check for shorts (e.g., orange and brown are shorted together when they shouldn't be), and the 2nd test is for continuity? Sep 28, 2022 at 21:58
  • 1
    @red.october - Yes, the first is checking for shorts, and the second for continuity. By "each pair" I mean each possible combination of 2 wires. So hold or clip one lead of the meter to one wire, then without moving it, touch the other lead to each of the seven remaining wires in turn. Now move the first wire aside and connect the first lead to another wire, and touch the second lead to each of the remaining 6 wires in turn. Continue the process until you've checked every combination. It takes a couple of minutes.
    – Mark
    Sep 28, 2022 at 23:31

As someone who has run a lot of Ethernet, here's my general "pins are out" checklist

  1. Crimped ends are notorious for having pins out. I've developed a methodology to make it relatively reliable, but the wires can still shift and you can easily get 1 or 2 wires that fail to reach the pin. Crimping is, hands down, the least reliable method to end your Ethernet, and you'll lose about 1" off the end every time you re-end it.
  2. Keystones are better (what manassehkatz called "jacks") because you can pull the wires out and punch them back in. More costly than crimping in the short run, but you get better reliability
  3. Don't rule out bad punch boards. We had our new building wired with Ethernet for not just the desks, but the cameras as well (PoE setup). I got 15/16 working on an older punch board, but the last one would not work (pin 6 was out). Re-punching and re-ending did not work (for this application, the camera end had to have a crimped connector because it was exposed). I got the wiring guys back in and they finally traced it back to the punch board. Pin 6 was apparently damaged and would not slice the wire sheath. They put a keystone on it and it has worked ever since.
  4. Damaged wires are a pain, but if the wires were pulled into place, it's not terribly hard to damage a few wires. If keystones on both ends with known good patch cables won't get a signal, you'll have to re-run it.
  • 3
    One other failure mode that is uncommon: In a jack (keystone), if you or the installer flips the punchdown tool, it can shear the inside of the wire off while leaving the remaining piece in the jaws of the jack. This might work for a while, as when you withdraw the punchdown tool, the two ends might be touching. But temperature / movement can cause this to fail intermittently.
    – gbronner
    Sep 29, 2022 at 14:10
  • 2
    @gbronner I did exactly this when I was wiring the ethernet in one of the kids bedrooms. The connections were slightly flaky, so I re-punched everything, with the Krone tool reversed :(
    – SiHa
    Sep 29, 2022 at 19:30
  • 3
    @gbronner those little side snippy scissors? Yeah they're great until you're upside down and backward in the dark, where left and right swap sides and you just undid the last 15 minutes of struggle by giving everything one last punch-down, THE WRONG WAY AROUND! Been there done that.
    – Criggie
    Sep 29, 2022 at 23:21
  • To be fair, the punchdown tool is usually symmetrical. It should be D shaped so you can intuitively remember which side is the cutter
    – gbronner
    Sep 30, 2022 at 1:28

I fixed it! Thanks for everyone's responses. It turns out the issue was that the ethernet wall jack in my office was damaged. I didn't even know that was possible. And it's not something you can see normally. I only happened to see it after I removed the wall plate and put it down on the floor at the right angle. I'm so glad I saw it before going through the trouble of switching the cables (which wouldn't have worked anyways, given where the real issue was).

I have no idea what happened - it almost looks like someone (previous owner) accidentally took a screwdriver to it. And wouldn't you know, the damage was to pins 2,3 and 4.

enter image description here


Your cable is probably bad. LEDs 2, 3 and 4 on a cable tester correspond to solid orange, green-white and solid blue wires of Ethernet cable (T-568A). If only one or 2 pairs (orange/while-solid orange, green/while-solid green, blue/white-solid blue, brown-white/solid brown ) have either 1 or 2 of their conductors broken cable can still be usable for 100Mbit/s but here you have lost continuity 1 of conductor of 3 pairs. Computer network uses each pair as a dedicated balanced signal line and 2 of those lines are needed for 10 or 100Mbit/s, 4 of those at 1000Mbit/s or higher speeds.

  1. If you recrimp and there is lack of continuity only on 1 or 2 wires then cable can be usable (with a non-standard crimping at both ends, 100Mbit/s only)
  2. If you recrimp and all connections are fixed, then cable is fixed and bad crimp was the culprit.
  3. If you recrimp and still 3 wires have no contact then cable is bad.

Infrastructure cables are crimped pin to pin.

There are also cross over cables which can be used to make a direct link between two computers. The data pair of wires are crossed over. Very useful -- sometimes. When you make your cable, do yourself a favour and label which type it is! If you pick up a crossover cable by mistake you can waste hours! My tester has an option setting for the type you need to test or you can find which type it is.

The other thing that helps a lot is a good pair of glasses.

  • Most things from the past decade or so autonegotiate just fine. Crossovers thus are a bit archaic unless dealing with archaic devices.
    – Ecnerwal
    Oct 1, 2022 at 17:23

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