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
