[theGeatZhopa]

If you can't disconnect all of them, then disconnect the one you want to find and look in the end which one isn't carrying current. So you somehow need access to start and end of the cables. Or you need a professional equipment with (inductive) tone generator.

Or, if you have access to the end of the cable in question, you can try to connect it to a pulsed current source (on off on off) and at the start simply check with a tester which one has on off on off..

Similar possibly is it to switch on off load in the end (like having pair of 2k W hair dryers) .. then in the start it's possible to measure the amperes with a Amperemeter or something with volt that should also change a little bit rhythmically?

Indirectly measuring the energy consumption (inductively) :)

Modulation of a signal on top a current, nahhh I don't know. To dangerous. Ask a professional, may be? Make your work be magically someone else' problem hahaha

[fefferkorn]

its actually another cable pair where some are connected and some are not. so i can use one wire for that. Its a telephone cable, so i wont be able to push high amps or current through, but yes, i can connect aome generator on our end and use an antenna, i know where the end terminates but incan not access it (its behind a wall plate with a key). someone already gave the hint with a fluke intellitone, which has the abillity to use the sensor as antenna, but i dont know the detection range (i probably need a.few.meters, but it has not to be milimeter accurate)

i can not open the cable in between, its not ours, i just want to use it on howto find out where and how it is layed