Micra (K12) fusible link blown - second time

[Andrewevans73]

I bought my 53 Reg Micra K12 about a month ago, at the time the guy who sold it to me told me that he had blown the fusible link when he replaced the battery. The other day my wife drove the car to drop our son to nursery, when she came to drive it home it would not start and it turns out that the 80 amp fuse on the top of the fusible link has blown. I have purchased a new part for 50 quid on EBay but I am worried about fitting it in case it blows again. I spoke with a local auto electrician to see if he would take a look at it and he told me that if the fault is intermittent it could be hard for him to diagnose and perhaps I should take a look to see if there are any obvious problems with the wiring - the problem is I don't know where to start looking, Does the fact that the fuse on the top top of the fusible link blew point to a particular area to concentrate my search on?
Any tips on locating the source of the problem would be much appreciated!