Although LUCAS has has been called the "Prince of Darkness" they left us with some great technical references that can help you locate parts info or trouble shoot your system Below are 2 very good doccuments to help.
LUCAS PARTS MANUAL 1948 - 1960
LUCAS TRAINING MANUAL SECTION:
01 - Batteries:
02 - Starters:
03 - Coil & Ignition:
04 - Generators:
05 - Generator Output control:
06 - Vehicle Wiring Circuits:
07 - Lighting:
08 - Accessories:
09 - Electrically Controlled Overdrive