Hi GP24,
Welcome to the forum, albeit under such unlucky circumstances. I think you've had an unusual event to your B-max. For a wiring loom to suffer such a catastrophic failure such that it needs to be replaced sounds very much like it has drawn a large current through it and damaged the insulation. Why this could have occurred is just conjecture at this stage until the garage investigates. I very much doubt and certainly hope that this is a one off event, both for you and for the sake of all other B-max owners. Good luck on a successful rewire and do re-post with hopefully good news soon.
Jaycee