I have a Cat 5 ethernet cable that runs from a stereo cabinet to an equipment closet. A couple dozen other identical cables run from other parts of the house to the same hole in my drywall in this closet. They’re not all well labeled. Originally, the cable in the stereo cabinet served as a telephone connection, with a 4P4C jack in the cabinet and the other end punched down into a 66 Block in the closet (question edited to show 66 Block photo).

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Now, I want to re-purpose that Cat 5 cable to serve as an Internet connection to the cabinet. I have already re-terminated the cabinet end with an 8P8C Ethernet jack, and I want to find the other end of this cable in the closet so I can connect it to our data network.

If the cable from the stereo cabinet weren’t punched into the 66 Block, I think it would be easy enough to find it, using an answer like “How can I find out which ethernet cable goes where?”. But if I were to use a Tone Generator and Probe, then I would expect for every cable in the house that serves our phone system (all of which are the same gray Cat 5, and all of which are tied together in that 66 Block) to probe positive exactly like the one cable I’m trying to find. Right?

Because of this, the only way I can think of to find this cable is to start pulling wire off my 66 Block. However, I don’t want to do this unless it really is necessary, because I’m fearful that I’ll mess up our home phone system in a way I won’t be able to repair. (One problem I foresee is that I don’t have a lot of extra cable length to work with for punching wires back down.)

How can I figure out which of the many Cat 5 cables that are punched down into the 66 Block in my closet is the one coming from my stereo cabinet?


4 Answers 4


Encouraged by the comments to my question, I bought a tone generator and probe (I bought a Fluke). Here are the steps I performed:

  1. I plugged the toner into the jack in the stereo cabinet and set it to generate a tone for the probe.
  2. I took the probe to the equipment closet and set it to the same icon as I had set the toner to.
  3. In the equipment closet, I passed the tip over all the cables coming in from the wall.
  4. The audible signal made it completely obvious which cable was the one I was looking for.
  5. Once I found the cable, I pulled its blue/blue-white pair off the block.
  6. I terminated the cable with an RJ45 keystone jack.
  7. I tested the pins with my little Ideal VDV MultiMedia Tester.
  8. I turned off my laptop Wi-Fi, cabled it into the equipment closet, and googled a word I knew wouldn't be cached. Called it a win when Google returned results.

Is your 66 block configured with bridge clips? If so, just remove the bridge clips and your many CAT5 cables will be isolated from each other, you can individually probe them to find the one you want, then reinstall the bridge clips.

I'm assuming your 66 block is not configured like that? How is it configured? Can you include a picture?

  • Something like this
    – Chris
    Jun 26, 2016 at 13:32

I zoomed into to the picture and I see writing on the plywood on either side of the punch down block. Many labels such as "master bedroom", "xxxx bedroom", "office", "study", and "kitchen" should surely help to distinguish where most of the cables are routed. Through a process of elimination you may be able to go right to the one to disconnect for testing in just one or two tries.

  • 2
    A toner would be the easiest way. Plug it in then hold the reciever in your hand and run your finger down the block when you here tone you are there. I use my finger it drops the signal level and pinpoints the corect line, if you use the tip of the reciever it can be hard to tell sometimes. If you are 100 based T you may need to shorten the wires to the block cat 5 twisted pairs being untwisted and looped like the photo shows may give some problems. 10 base it would be fine but most everything is 100 now.
    – Ed Beal
    Jun 26, 2016 at 14:11
  • @EdBeal, thank you for your encouragement. I bought a toner, and the rest was so easy I felt like I was cheating. Jul 4, 2016 at 21:46

I know this is an old question, but....

I found this very useful.

  • It includes a tone generator and a tracer, you can follow the cables.
  • It can show if all wires are connected properly.
  • It can show where a break is.
  • It can make the light blink on the port on a switch blink, useful if you need to identify an outlet without unplugging everything.
  • It have 8 remote dongles, you can use to identify and test 8 cables without having to run between your outlets and junction cabinet.

Look for NF-388, around €50-€60 on eBay

[NF-388 network tester[1]

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