I am trying to rewire the telephone wires in my home, and I appear to be not getting it. I have extremely familiar with running cat5, as I use it all day long for my job, and thought telephoney was just as straight forward.

I have standard 4 wire telephone wire. It's got yellow, green, red, and black. On one end, I have a punch down terminal inside the wall in a wall plate. That side is wired correctly, according to the keystone diagram. I actually have two of these coming from two different rooms. I then combine them both into one using a splitter like this:


That goes directly into my comcast business modem/phone. I have a cable checker that I use for my coax and rj45 connections, and it also has voice testing, too. When I check any of the cables, it shows up as open on all wires, and I can't figure out why.

I thought the wires needed to be the same all the way through, but in looking at how the wire is bundled, that doesn't seem possible. Putting the connector on both ends, then comparing the ends shows that the two inside wires are reversed. (One end is yellow, green, red, black, the other is yellow, red, green, black). I have tried remaking all the wires all the way through the line and cannot get the line to work. Even testing with a phone shows that the line is in use.

What am I doing wrong?

  • Is it possible the cables just weren't very well made? That twist seems wrong. Is your source a competent domestic supply, or is it el cheapo Anazon Marketplace shee jin hua? I realize that link is just an exemplar of the shape of the item. Oct 14, 2018 at 16:18
  • I got the wire from Menards and the connectors as well. The splitter also came from there and is rca brand. When holding both ends of a cable so the connectors are facing the same way, the wires are in fact reversed in the middle.
    – Ex0r
    Oct 14, 2018 at 16:24
  • The reverse is common with phone wires and should not make any difference. All voice equipment I have worked with, and even a lot of digital (not VOIP) phone systems handle polarity reversals automagically. Oct 14, 2018 at 21:52
  • @manassehkatz That's what I thought, but am boggled why the phone doesn't work.
    – Ex0r
    Oct 15, 2018 at 2:17

1 Answer 1


First of all, you don't need special telephone wire. You can use the same wire you use for networking - e.g., Cat 5, Cat 5e, etc. I used to use leftover old Cat 3 for telephone wiring, but once I went through all that, I switched to using Cat 5 for everything even if it costs a little extra for the phone wiring than absolutely necessary.

Telephone wiring does have polarity - i.e., red/green is different from green/red. But it does NOT usually matter.

The middle pair on T568A/B wiring is the same as the pair (aka red/green) for standard phone wiring. You should use RJ11 (1 pair = 1 phone line) or RJ14 (2 pair = 2 phone lines), but you can actually use RJ45 network jacks and just connect a pair to pins 4/5 for one phone line, though the patch cables may not hold as well as with RJ11/RJ12.

Troubleshooting: Ideally you should have three tools to test:

  • A telephone test set. But for very occasional use, you can simply use a phone - preferably a phone that does not require any power beyond that supplied by the phone line. Plug it in at each point that you need to test, and if you get a dial and can make a call then you are good, and if you can't then you need to keep working on it.
  • A tone generator/detector. Mainly for checking when you are trying to figure out which cable is connected to which port. Keep in mind that there can be false positives - i.e., it is good for figuring out which cable is which, but not so useful for figuring out which pair is which.
  • A wiring tester. This one is just a random example - there are many different types but basically something that lets you put a remote on one end and a master on the other and see which wires are connected correctly, reversed or not connected. This is extremely useful for Ethernet cabling, but helps with phone cabling too.

Just work through it step-by-step. First check the Comcast modem and make sure a phone (or test set) works there. Then put in the splitter and make sure each connection works there. Then put in the next patch cable and check there, then the long cable run to another room, then its patch cable, etc. At each step if you can't see the problem then use the wiring tester to see what, if any, wires are actually connected.

I also recommend NOT using a long cable with plugs on the ends. Wire up (same for Ethernet) jacks on each end and use short, easily/cheaply replaceable, pre-made patch cables for jack-phone, jack-splitter, etc. Properly installed jacks rarely go bad, but plugs on the end of long cables often go bad.

  • I am using an ideal cable tester. It tests coax, voice, tone and data. No matter what configuration I use, I get bad readings on the tester. The phone I use is 100% battery operated and with the exception of plugging right into the modem, I get 'line in use' on the LCD display on the phone. This is regardless of what combination of wiring I use. I've checked that all the wiring is consistent, and with the exception of the red and green wire swapping location with each other, everything else is identical.
    – Ex0r
    Oct 14, 2018 at 15:19
  • Test it a piece at a time. Use the Ideal tester on a simple phone (i.e., 2 or 4 wire) patch cable and see if it gives good results. If it doesn't then that isn't the right tester for the job. If it does give good results, then test with a patch cable + the splitter to test both 1/2s of the splitter. If that is good, then add in one of your long cable runs. Etc. Once you have all that straight, then plug splitter into modem and phone into splitter, then work your way out one step at a time. Oct 14, 2018 at 16:03

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.