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I moved into this 15 year old house about a year ago and there's a RJ45 wall jack in my office (2nd floor) and there's another one in the living room near TV. I'd assume there's planned in for TV to use Internet. I have not seen any other RJ45 jack anywhere else through the house.

So I plugged a cable from my router to the jack in my office, and I have no signal on the other end in the living room (I plugged a switch). I took out the wall cover plates on both jacks, and the they are the same type of Cat5e cables. Is there a easy way I can test these?

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    there are testers for ethernet cables, you can use those with 2 little patch cables (that are known to be good)
    – ratchet freak
    Feb 1, 2016 at 10:59
  • maybe you can cut an existing cable in half and apply some continuity across the wires? :)
    – rogerdpack
    Feb 1, 2016 at 15:00
  • I moved into a house of about the same age, and the 5-6 Cat5 drops that were in the house went up to the attic and were just hanging there. One of the drops was hooked up to a phone line coming from the box outside, but the others were just left unconnected.
    – JPhi1618
    Feb 1, 2016 at 15:23

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My guess is these two Ethernets don't connect to each other; they both go to some third location yet undiscovered. Back in the old days, there was no WiFi, and there was an Ethernet run to everywhere you wanted networking, the runs went to a single location where you had a switch, router, DSL modem, possibly a server etc. This equipment took at least a shelf or two and had a cluttered, cables-everywhere hacker aesthetic. Probably near a phone line outlet since DSL was still king. A homebrew version of the "wiring closet" you have in offices today.

I would look at locations in your house where that would make sense or be likely to be "wife approved". It won't be a place you would ever want to put a TV.

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Your testing method seems reasonable and probably rules out continuity between those two drops. (The exception might be if your router or switch don't have Auto MDI-X sensing and you needed a crossover cable, but that's unlikely as most devices made in the past few years should figure that out automatically.)

So if these two drops aren't directly linked, where do they go? Most often these run to a basement, attic, or closet. Possibly (but not necessarily) wherever your home's telephone wiring terminates. As a first step, try to figure out where the lines go - perhaps you can find a common termination point and locate your router or switch there to supply the drops.

If visual inspection isn't working, you can use a tool called a wire tracer or tone-and-probe kit to track where the cables go in your walls. The tool has two pieces: a tone generator and a probe. You'll either plug the tone generator into an RJ45 port, or open up the drop and clip the tone generator to a wire in the ethernet cable. The toner generates a signal that flows through the cable, effectively using the cable as a radio broadcast antenna. The probe then picks up on this signal (usually a beep or siren type tone) and replays it. You can move the probe back and forth along your walls, and identify the path the cable is taking.

Basic tone & probe kit

Tone and probe kits are not super cheap tools, but a basic comms-oriented one can be had online for around $25 (example). I have a cheap Harbor Freight one that I've gotten a surprising amount of use from in various wiring projects.

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