Check out the Vanagon archive thread beginning at

http://gerry.vanagon.com/cgi-bin/wa.exe?A1=ind9810c&L=vanagon#64

In other parts of the world this is the space for the tail
light, the outside space used in N. America for taillight is
for brake light (or I have this reversed).  This inside big
space used in N. America for brake light is used in rest of
world for rear foglight.

Still haven't figured out how to convert mine.