Icepack, you can download the 2006 - 2014 Classics parts book
here. It includes various wiring schematics at the end including the rear loom for your car - look for V6 Ford rear harness, likely the last one, it will be similar if not identical. As suggested the rear fog circuit is via a headlamp module which may be seen in the dashboard schematic assuming this is applicable to your car, otherwise part of the infamous PCB. Note the former has its own standalone 5 amp fuse and inhibits fog light until headlamps selected.
You can certainly check the rear wiring tracing the generically coded red/yellow wire but have you checked the 7.5 amp rear fog fuse 5? Check also all related connectors, I counted six! Basically you have the switch which grounds a connection on the headlamp module which conditionally passes current from feed fuse 5 to a red/yellow wire, this continues via dash connector to main loom then on to rear loom and light connectors. You will note there are two of latter to allow twin reverse and/or fog lights to suit differing country regs.
Regarding interpreting the loom schematics, all the info you need is present providing you have the patience to trace the wire codes, a colour abbreviation followed by a unique number.
