Nope, it's definitely not the trailer plug. I have one too though.
The trailer module plug is below that metal shelf part. It's a green plug like this. It could be taped up with the rest of the car wiring.
The yellow/red wire from F26 comes to a grey plug, inside the foam. The trailer wiring from the socket plugs into the grey plug then loops back out as a red wire and to the module. If you don't have a fuse in F26, it's likely you won't have the canbus wiring either. The green plug comes from the car wiring. this is only for the genuine Ford dedicated kit.
Well that's poo, I've had another look and there's definitely no other connectors etc in that area. It seems as though there is no wiring whatsoever for a pdc retrofit either, oh well I'm stuck with the rubbish ones that have been fitted.
It could be for the rear sub which they get standard I think on the USA models. I will see if I have one as I may need to have a look in there as I put the trailer on the car tonight and no electrics. Tried the big trailer and the same. At least I know my car has some form of dedicated electrics as I could see the module but it would appear that someone has tried jamming an extra wire in the connector that's fitted to the car and I don't like the look of that. Worse than seeing a scotch lock lol. Will pull fuse 26 tomorrow when it's light but it would take a lot to blow a 40A fuse when all I ever pull is a trailer.