Not sure that would help Robbie as info gleaned from looking at several 3.7 Roadster diagrams. I have looked at the GoMog wiring diagram you referred to though and it is different. Unfortunately it also lacks the detailed diagrams for individual aspects of Roadster electrics shown in the 2014 on parts manual. Nevertheless I think you should be looking at the 9 pin connector behind dash from steering wheel area to loom.
You can download wiring diagram for earlier Roadster
here.
ETA: Horn push trigger is purple/black cable, dipped beam feed blue/red cable from connector to loom. Hopefully this will help in fault finding.
