This is not exactly related to cameras, but if you also do a lot of audio recordings or make custom cables for your cameras this trick can be very useful. I know many of you guys are into the electronics. So I think it can be helpful.
I hope this stuff is OK in the hardware section of a forum. I invented this interesting method of checking cables myself, and never saw anyone doing this, but similar techniques are used in industrial applications.
https://www.youtube.com/watch?v=YsIAdSP0_xw