John
Many thanks for your detailed response, for someone like me who thinks a minor miracle has occured when I switch a light on, your help is invaluable.
A bit more detail building on your post (see photos below):
Ballast resistor relay - has 85,86,87 but also 30/51 - does this make it incorrect?
Coil - photo shows full range of numbers
Ballast resistor - see photo, part number as you quoted
Alternator - see photo, best I could get whilst in situ!
Once again many thanks and obviously if you can add any more info please do.