The understanding of the front to rear wiring run is easier than the main loom; there are less variables throughout the production run 1933-37.
These images show a 1937 car and the start of armoured wiring leading from the under-dash area backwards – for the functions of stop and rear lamp, and fuel sender.
Here is a 1933 car pre-restoration:
The loom descends from the dash, clipped to the underside of the O/S dash cubby, behind the trim panel to emerge in the drivers footwell. Note the treatment of the wooden retainer for the trim panel in this area:
The loom runs underneath the car and comes up behind the door pillar, running above the floor to reach tail light and fuel tank sender. There is only a single wire which branches off to the sender via a 5/8″ grommeted hole in the boot floor prior to the wooden divider between passenger compartment and spare wheel space.
The images below are from a 1936 car. Note the grommet into the boot as being from when there was just one rear light. Do others have evidence of boot grommet points in the same place?
Thanks to Ian Williams, Chris Gould, Nick Boorman and Dave Griffith for descriptions and images.