The main area where the wire breakages tend to be, in my experience with 2 x Z3's anyway, is where the wiring loom is held in place by the plastic clip on the left hand boot hinge.
I actually repaired my silver zed only last weekend. I removed the plastic clip altogether and have tethered the loom to the hinge with a cable tie. I'll take a photo later and edit this post.
In my case 5 of the nine wires were broken and were probably only kept together because they were tightly wrapped in the loom. The only symptoms I had was the intermittent operation of the central locking and setting of the alarm.
It was an easy fix though, only took about an hour all in.
The wires to the upper brake light
Plastic clip removed