[Spits] Haynes manual wiring diagram

[BJ8 Healeys]

Hello, Spitfire Pilots -
 
I'm not a Spitfire owner and usually hang out in the Austin-Healey world,
but am posting this question to help a friend who does own a '79 Spit but is
not on the list.
He has the Haynes manual for 1962 - 1981 Spitfires.  On page 266 is Fig.
10.66, the wiring diagram applicable to North American LHD 1500s from
commission number FM95001.
 
Can anyone help us interpret some of the symbols on this diagram?  There
doesn't appear to be a definition of them in the manual.
Specifically, the symbols are circles.  Some are open circles, some are
split by a line into two halves, some are split by crosses into quarters,
some have one half blackened or two oppposite quarters blackened.
 
Thanks for the help!
Steve Byers
Havelock, NC