I've checked the wiring with ISTA diagrams and things seem to be as they should.

I've checked the 7 pin trailer socket and all connectors are doing what they are supposed to (left indicator gives 12V at the correct pin etc etc).

I've tested continuity from the trailer control module to the trailer plug and all tests as it should with the correct wires going to the correct pins.

It's like the Trailer Control Module is defaulted to trailer connected?

I just don't know where to go to from here. I've spend hours and hours on this and all pins go to the right location.

The only other thing I can think of is the amount of soldered joins is creating some resistance to think it is connected? I soldered properly each wire and shrink wrapped each of the individual cables (all 15 of them).