Just been having a look at the Haynes manual David
In the engine bay on models circa 1989, the Blue wire goes to the alternator .... Warning light, by the looks of it !!
Can't find any reference to SW in the colour codes ?? .... This term quite often used to denote Switch ( In electrical speak )
Here's the Haynes Colour codes
B = Blue
BK = Black
Bn = Brown
GN = Green
R = Red
RS = Pink
S = Grey
V = Violet
W = White
Y = Yellow
That's the best info that I can find mate
