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Tracing cables under floors/behind walls(r/sysadmin)
What you need is a tone generator and wand, aka: a fox and hound.
The toner is plugged into the line at the wall, and sends a voltage down it at a low frequency.
Most toners also have a spiked alligator clip that can connect a line without disconnecting the wire’s ends.
The tone detector (probe, wand or hound) is able to convert the magnetic field from that voltage into an audible sound.
Just wave the wand near the block/panel, and it starts screaming as you get close to the line you’re toning.
This is the one i use.
Edit: I’m curious about what your job title/field is. Most people in IT learn about these on the first job site.