what you want is a power probe, you can insert or complete the circuit with +12v or ground, it's pretty handy, if you understand electrical, and it sounds like--- probably not.
https://a.co/d/eP7e0g0
truth is, for all the lights to be out, you probably don't have a "break in the cable" this is pretty rare unless someone was drilling thru some stuff and hit a harness.
It's likely you have a bad ground, since all the cluster lights share a ground somewhere. Can you take some photos of what you are seeing? Most of these issues show up at one end of the car, front cluster or more likely the rear.
When was the last time they worked, what happened since?
Otherwise, google or YouTube 2001 Z3, chances are someone had the same problem and wanted to tell the world about it.