Update, the +12V off the light switch at "fuse 12" (the second fog light position) it is not there. The fuse (#12 according to the service manual wiring diagram) isn't even addable (is that a word?) its not cut into the assembly. They must have two distinct part numbers for the domestic and export XF's with the export model having that fuse 12 output for the rear fog light.

Haven't given up though, will have to look over the lamp module real closely to see if anything "connects" to that switch position (the second pull of the fog light switch position).

Love playing with this car!