No real ideas but when I bought a new +8 in 2002 the dealer gave me a spare main fuse and said there had been quite some incidents of them blowing so best carry a spare, mine never did and not heard much about it since. To pop a fuse of that rating would require a serious grounding of feed or just maybe a faulty fuse, however if that were the case it would have blown long before now. I would be inclined to bridge the fuse holder with lower rated fuse wire, turn on the ignition and then move and squeeze the harness wherever you can get hold of it especially on sharp bends over corners like the bulkhead under the bonnet as that was a well known rub point some time ago and see if you can get the lower rated fuse wire to blow. Good luck and sorry that's all I can think of.
