Check out this thread on the 986 Forum:
Does anyone know which is the vss wire on an 02 with Bose? - 986 Forum - for Porsche Boxster Owners and Others Post #14 shows some pictures of the reverse wire.
For U.S. cars, the wire is located under the driver's seat on the left. I realize that you have a right hand drive car, but I don't think Porsche would need to relocate the wiring to the other side to accommodate the change in driver position.
There is some other useful information in the thread and some links that may help with your project.
Good luck.