Thanks to Jeff@vanagonparts.com, we're farther along the trail to foglight
wiring.  Seems the ECode rear lights have the fog lenses and as we all know
the DOT rear light has a reflector in that location.  On personal inspection
the ECode rear light panel (bulb holder) has an active socket in there WITH
a lamp installed.

The US spec wiring harness has no wire or connector that mates with that tab
on the light panel.  There is also an open pin in the cylindrical connector
that interfaces between the lighting harness and the chassis harness.  It is
my guess that that location is the one that could be or is used to run the
rear fog light.  I'll do a little checking on my harness to see if there is
a chassis side jack element that mates with that pin.

There are lots of elegant solutions to the problem.  One could replace the
backup light on the Driver Side with an LED red lamp that will perform the
rear fog function and add two REAL backup lights available at the local
FLBLPS (known as fog lights) to the rear to provide the kind of lighting
that Unca Joel has to jacklite the possums.  Possums are notoriously slower
than vanagons and to avoid running over 'em when parking you gotta have good
backup lights.

Or add a cibie 40 rear fog light or a rectangular cibie rear fog light or
something similar but you still have to solve the signal path.  Long ago
hella or bosch made a nice one for Porsche. 5x8cm or such.

In the interim, when foggy days happen I'll stay home and pet the cat or
troll a weenie for the neighbor's microdog.