Whilst this article is not specific to the pre-war Austin Seven it may provide extra information, and/or clarify, that which is available from other sources. Articles specific to the Austin Seven are in sections of The Austin Service Journal; and those written by our members are in Technical Articles.
NB:
Fig 2 is purely explanatory and shows a
simple wiring diagram for headlights with a single fuse. If a bulb
goes and takes out the fuse, then BOTH lights will go out. This is
not good practice and a separate fuse for each headlight would be
advisable.

Wires and Terminals - How to ensure their electrical efficiency From The Austin Magazine, August 1933
Wiring Diagram Simplified From Practical Motorist and Motor Cyclist, September 1954.