Thanks for this post with all the images, drawings and information. I have an MY17 LD5 SD4 - I purchased the Tekonsha 3035-P from Amazon for $16AUD and got it fast freighted for $17AUD - it arrived in less than a week! Job done in no time.
Just an update - I did not need to adjust the wiring in the 3035-P plug - it was already correct for the socket under the dash.

I've not calibrated it yet - but everything appears to be working well and configuration was correct on a multimeter.