Richard what a great help you are. OK I'm feeling more positive having seen this drawing . I wondered where the second wire on the non power side of the fuse went - I could just see it disappear into C58 ! OK so it looks like I've only isolated 4 out of 9 options. Now I know where it goes I'll disconnect / them and see where it goes.
In answer to your question 'under what conditions does the fuse blow'. Very good question. When I change the fuse and start the car it seems fine , when I drive , by the time I've got home it may have blown. But if I start the car from warm I get the impression (although I've only gone through 3 fuses so far) it can blow. My instinct is telling me it could be engine temperature related - ie if everything is hot there is a greater propensity for it to blow . As I said I've only gone through 3, but it almost feels like there is a short when it is hot. I've got a load of fuses arriving and then I will let the car warm up. Stop it and then start it again - I have a feeling this will blow the fuse. If this happens ,which I hope iy does , I will then disconnect the solenoids (and purge valve) and see what happens next.
BTW - where is the purge valve? I've never had a any reason to really go and look for it !!
Please could you let me know how I could get hold of those diagrams. I've always been a bit apprehensive with the wiring on the Mogs. All of the ones I've owned at some point in their lives have had electrical issues. the roadster has always made me nervous , it has a lot of electrics to go wrong. I use mine every day , wind , rain , ice (when I feel brave) .,
Thanks again for taking the time to help me.