[russellw]

Let's step back a bit.

I believe it's actually a 13 pin plug (the alternate being a 7 pin).

Power for the plug is sourced from the module itself. There is a Blue/Red feed wire into the module that provides power so check that you have 12V there. It's power source is Fuse 26 in the engine bay junction box.

I'm not sure whether the trailer module has to be configured in WDS but the fact that you are getting some response would suggest not.

A quick check is to read the voltage on Pin 9 or 10 as they are both straight 12V feeds.

Diagrams below.