I have a cable. Inside the cable are approximately 100 wires, all running
parallel and not twisted or otherwise intertwined. The cable is about 2cm in
diameter.

Signals are sent across the wires. Usually only a few at a time and usually
briefly. The rest of the time, the lines are dead.

The signals are very weak. Approximately 50-80 millivolts at maybe 4-20
milliamps.

What I would like to do is get a rough idea of which wires signals are going
through and when, from outside the cable. I don't need to know specifically
which wire, but just roughly where it is in the cable.

The idea I had was to create 3 coils that I could run parallel to the cable,
in a triangle around the cable and then try to do a rough triangulation. Is
this feasible with the extremely low voltage and current? I cannot do
anything inside the cable. This must be external.

Thanks.

Pete