I have a Cat 5 ethernet cable terminated with a RJ45 Ethernet (8P8C) jack in the Master BR that is serving as a telephone connection. The other end of the cable is punched down into a 66 Block in the basement. This was a part of a structured wiring setup from year 2000.

Now I want to re-purpose that Cat 5 cable to serve as an Internet data connection. I want to find the other end of this cable in the 66 block so I can connect it to my internet network. Once identified, I will terminate that end with a RJ45 connector.

I have used a Klein Tools Tone Generator and Probe with the RJ45 connector inserted into the RJ45 jack in the Master BR, however every Cat5 cable in the house that serves my other phone jacks tied into the 66 Block are getting the tone. The tone is also heard through the phones. The tone generator is set to "tone".

How can I trace and isolate this single Cat5 cable without getting tones from the other cables?

2 "66 Blocks

back of RJ45 jack

  • Ecnerwal - See added pictures. Thanks for your response.
    – cpearcy
    Commented Jan 31, 2023 at 0:02
  • 1
    I would suggest removing the black twist ties from any cable you plan to actually use for Ethernet purposes. I have had issues (granted it was several decades ago) with intermittent network connection issues - the problems went away when I removed the twist ties that were holding extra cable neatly looped. Used Velcro™ ties to hold them in loops and never had problems again. May not be an issue with 5e/6 cable, but... why take a chance?
    – FreeMan
    Commented Jan 31, 2023 at 13:52
  • 1
    Thanks for you suggestion. I did remove the twist ties that I placed temporarily.
    – cpearcy
    Commented Feb 2, 2023 at 21:58

2 Answers 2


My assumption is that all the jacks in your house are connected together at the 66 block for analog voice. You had one analog phone line coming into the house, and all jacks with a phone plugged in would ring at the same time. Very standard when wired for voice. At least you have all the jacks installed as home runs back to one place instead of connected in a long daisy-chain! That makes the cables possible to repurpose for Ethernet.

In order to figure out which cable coming into the 66 block is the one you are sending the tone on, you'll need to isolate the house cables from each other. The best way to do that at the 66 block will depend on how they are connected. I've done them with bridge clips and with hookup-wire jumpers. Bridge clips will be easy to see because they are big metal clips that connect two contacts in the block. Pulling them out with pliers is easy. Hookup-wire jumpers are a little more difficult to pull off, but not too bad, especially if you have needle-nose pliers.

If you can include a picture of the back of the RJ-45 jack/plate and a picture of the punchdown block, we can zero in better on how to get this done.

When putting these into use as Ethernet jacks, you'll want to terminate each cable with an individual keystone jack that can either hang free or click into a small patch panel. They even have 12-jack patch panels that click into the same mounting bracket your 66 block is in now, if you want a clean look.


Now that we can see the blocks, we can see what is going on.

The yellow cables are presumably your house wiring. The blue ones are presumably cables that come in from a network interface outside the house (where the Telco service comes in).

Each cable is punched down to the outer "hooks" of the 66 block, pair by pair. The Blue/white is default for "line 1" when used for voice. Each set of 2 "hooks" in horizontal line are connected together inside the block, thus to cross connect to your jumper wire, you'd punch it down to the inner matching "hook".

Unless you're really dedicated to maintaining this wire and own a 66 punchdown tool, I'd suggest pulling the yellow "house" cables off the blocks and reterminating them with 8P8C jacks. It's just much easier to deal with unless you really want to pretend you work for Ma Bell. :)

  • Chris O - you're right, the telephone wiring is standard for voice and all the jacks are installed as home runs. Of note, I did have 2 analog phone lines coming into the house however currently only have service on 1 line. I don't believe I have the bridge clips you mentioned however just added a picture for reference. Thanks for your response.
    – cpearcy
    Commented Jan 30, 2023 at 23:53
  • I would leave the 66 blocks well enough alone (other than removing the cable of interest, once identified) since there's an active landline and they work quite reliably for that.
    – Ecnerwal
    Commented Jan 31, 2023 at 1:15
  • @Ecnerwal True - they work great for voice, but RJ-45 jacks work just as well for voice, plus jacks have the advantage of being reconfigurable by simply changing the patch cable rather than rewiring.
    – Chris O
    Commented Jan 31, 2023 at 15:16
  • If it ain't broke, don't fix it. Every time you mess about with reconnecting cables, you introduce the possibility of error. So dismantling a working, in-use voice setup with quite a few jacks for the sake of "ohh, I have patch cables now" when only one ethernet connection is desired is dubious - doubly so for someone inexperienced with the process. I do work on places with 50 year old 66 blocks still working fine for voice. There's no indication of adding to the (extensive) voice jacks in the question, just repurposing one cable to ethernet.
    – Ecnerwal
    Commented Jan 31, 2023 at 15:36

If you'd rather not undo your phone setup (might be desired if it's still in use for a landline) you can connect to one of the unused pairs in the cable of interest, assuming the typical voice on 4,5 blue/white setup, other pairs not punched into anything.

Either strip the ends and clip on to a different pair, if your toner does that, or pull the blue-white pair from the one jack you want and punch in one of the other pairs (or all of the other pairs) and connect your toner. I've done it with a 9V battery connected to the pair of interest and a voltmeter, in the absence of a toner.

I'm making usual assumptions (house is not wired for multiple phone lines, standard use of colored pairs, etc.) which could be subject to revision if you post pictures of what you actually have. You may need to upgrade the old 8P8C jacks to 5e or better for fastest ethernet speed you can get from the cable you have (it might do gigabit, even though it's only 5. But older jacks might limit it to slower speeds.)

Edit, Add: Now that we can see pictures, it looks like whoever put this in punched down everything. However, the green and brown pairs are not interconnected so you should still be able to track down the cable you want without disturbing your remaining analog phone line.

If your tone tester has alligator clips, (most pictures for that tool description show a set) clip them on the 66 block where a green or brown pair attaches, [so one to the green (or brown), one to the white-with-green (or white with brown) right next to it] and then find the cable they go with in the house. Update/improve/clarify the labeling if it does not seem to match what's there. I'd expect one of the ones labeled MBR would be your best bet for the master bed room. That way you don't have to mess about with disconnecting wires at the far end, nor tearing up your extant analog telephone wiring that's still in use.

The wiring to the jack will, at minimum, need to be removed, have the twist restored, and be reconnected, even if that is a 5e jack (which it isn't, being from 2000 - so get some 5e or better jacks.)

  • I just added a picture. The house is wired for 2 lines however currently using only 1 line. Thanks for your response.
    – cpearcy
    Commented Jan 30, 2023 at 23:55
  • The labeling would appear to offer the opportunity to cut down the search time a great deal.
    – Ecnerwal
    Commented Jan 31, 2023 at 0:04
  • @Ecnerwal Unless the labels are leftover from wherever those 66 blocks used to live. I used a lot of decommissioned telecom stuff at home and sometimes the old labels don't come off.
    – Chris O
    Commented Jan 31, 2023 at 0:09
  • The labels appear household, not industrial or office - and they go with the relatively unusual (in telephone work) punching in of all 4 pairs.
    – Ecnerwal
    Commented Jan 31, 2023 at 1:01
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    Update: I was able to successfully identify the correct Cat5 cable in the 66 Block by guessing correctly that it was the "MBR DSS" on the 66 Block. I was able to confirm it as the correct wire with the tone generator and probe only after I removed the cable from the 66 Block and retested. I replaced the RJ45 jack and wired with the T568B configuration and I now have successfully re-purposed the Cat5 cable to from a phone to data cable. Thanks everyone for your support.
    – cpearcy
    Commented Feb 2, 2023 at 22:14

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