Have we missed anything?
you've covered everything i can think off brit. Are there any wires that might be for the washer motor?
just my 5 pence worth, and I'm not an expert by any means, but i'd have thought you can work it all out with a simple continuity tester. anything that you can trace back to battery -ve terminal is earth, and anything that goes back to the +ve terminal is live, right?
once you know what's +ve and whats not, then i'd have thought you can chase the wires back to the fuse box to identify which system they are for?
A day, or even a whole week of evenings, playing with it has got to be better than $700