Simon,
Just to clarify, although I was very grateful for your suggestions regarding the photos, before I was able to put them to use it was actually Pete at
[email protected] that sorted the post out and edited in all the pictures and video.
Regarding whether the standard fan current consumption could have caused the feed wires to have heated up sufficiently to bond together, which they most certainly had, I cannot say. The fact that an 80A fuse was considered necessary for a 450w fan motor that at max I understand might require 37.5A, strikes me as quite a lot of leeway and possible overload of the wiring in question.
I will leave that discussion to those who have a better understanding of physics than me, but meanwhile I'm happy to try using a fan that has apparently proved to be adequate at less than half the wattage and current consumption.
I don't think I've gone off piste with cars at all before, partially out of respect to engineers who know much more than me, so this deviation from the original spec is a first...