Thanks fellas,

Yep I'm sure every wire is correct. The weird thing it sounds like the Trailer Control Module thinks there is a trailer connected and is throwing the fault because there isn't any load on the circuit from bulbs.

It's also possible that the reverse lights are supposed to not come on with a trailer connected?

I checked pin 13 which is the Canbus to the LCM and I get 12v with the TCM disconnected and 10.8 with it connected.

Strange.

The second hand TCM I bought could also be faulty I suppose.

Appreciate the help!