I believe Honda and Toyota are both facing class actions over the use of soy in the coating of electric cables, which is said to attract mice (and possibly martens?) Coincidentally I spent this morning cleaning all manner of stuff off the engine block and around the plugs of our Hyundai, after it smelled as if we were driving a mobile chip shop. On opening the bonnet we found small slivers of bone, feathers, a small fish backbone and various seeds, which had been 'cached' on the engine! It absolutely reeked. The car is used almost every day so it must have happened very quickly. There was also some evidence of cables being chewed.
I had heard that there is a make of insulating tape impregnated with something that repels rodents, but none of the hardware shops I visited in town had heard of it. (You can get it in the UK apparently.) I am reluctant to put mothballs in the engine bay, as they are highly flammable (or they were, when I were a lad, as we used to set fire to them
) so my better half came up with an idea that, I hope, will work. After re-wrapping the cables with ordinary electrical insulating tape, we rubbed chilli juice over them. Hopefully the mice/martens will find chilli too strong for their liking. On the other hand, they just might like curry, in which case I'm in trouble. So Daisy, you could try leaving some extra hot chillies around your garden -- a Dorset Naga would do the trick if you can get it!