re:  I cannot, however figure out where the red wire is supposed to
attach. It looks as though it must be a ground wire ...

Blasphemy!

All German vehicles follow the Bosch wiring convention.  Red always
means permanently hot wire, i.e. directly connected to battery, no
switch.  Ground wires are always brown (ground=earth=dirt=brown).
Have owned so far VW, Opel, BMW, BMW motorcycle, Mercedes--it's always
so.  This book covers it (and a lot more) -
http://www.rb.com/bosch/h001/h001.htm

Try also http://www.rb.com/bosch/h169/h169.htm