Where my cable comes into my new apartment there are a number of coax cables labelled with rooms that don't have outlets. I bought a toner and probe (Fluke Pro3000) to try to trace them in the walls, but I'm having trouble getting it to work.

First, I attached the toner's black lead to the internal wire and the red to the connector outside. The probe sounds when it's near exposed coax (and near an outlet when I tested it on a known cable), but the tone disappears as soon as the cable goes into the wall. I also tried red to internal wire black disconnected with similar results.

On the advice of The Internet, I then tried red to internal wire, black to true ground (the handle of my fuse box, which I assume is grounded). This lit up EVERY coax and telephone wire in the entire apartment with very audible tone through the wall, making it impossible to trace any given one.

Any thoughts on what I'm doing wrong? Clearly the probe is capable of picking up tone through the wall, but I need to narrow it down to individual wires.

  • Have you tried playing with the sensitivity dial when you have 'every' cable lit up and when you have simply connected to the end? Is there any chance the cable dives quickly through a wall or floor, thus making it hard to trace? Commented Sep 24, 2016 at 14:52
  • With the sensitivity on max, I still wasn't picking up anything when simply connected. It's possible it goes under the floor (although it's a one floor apartment in a complex, is that common?) but even near a known outlet it barely detects it in the wall
    – mrjogo
    Commented Sep 24, 2016 at 15:10
  • Never used a fluke pro3000, my fox and hounds are much older units. But for coax, I have made a pigtail out of a female connector with the center and shield shorted. Then clip just the signal lead to those. Commented Sep 24, 2016 at 16:05

2 Answers 2


The point of coax cable is to protect a weak signal from outside noise. That also protects the outside from a signal on the coax.

What you need is something that puts out a signal that can be picked up when connected only to the shield, so there isn't a balancing counter-current on the interior conductor.

I am fairly sure such exist; I can't recommend any specific products.


It is a bit hit and miss but try this.

Connect one clip of your tone generator to the shield. Connect the other clip to actual earth ideally or a fake earth, the nearest convenient large chunk of metal.

It has a tendency to jump to other cables though when used like this.

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