Turns out the kit they sent me only fits up to 2011 model, not 2012 (as it was advertised!). So, this explains why it has been such a head wreck to install. Thanks for everyone's help. Hopefully the correct part will be easier to install

Thank you!

This is all the wiring I've been given. The white plug fits in the ECU so I assumed I was looking for a plug in the car that fits the brown plugs. I have followed the wiring all the way back to the dashboard. The only place I haven't looked in under the passenger seat as it seems some wires go off t...

I did find about 3 plugs along the wheel arch under a panel. One of them turned off the left indicator when unplugged but the wiring I've been supplied with doesn't fit in that plug. Maybe I have been sent the incorrect wiring harness?

So I ended up removing the back seat incase it was there but it's not. Unless the plug is hiding somewhere under the carpet in the rear seats, I can't figure out where else it would be because the cable isn't long enough to go too much closer to the front

It has a grommet to run it outside, just not caught in the photo. I called a towbar shop and they seemed to think I'd have to remove one of the seats to access the plug. Does that sound right?

I've removed the left boot trims but there's no plugs that fit the same as the wiring harness. Do I need to remove the rear bumper bar to access it?
This is a photo of the wiring harness and the wires just behind the rear left wheel arch

I have bought an OEM towbar and wiring kit from an auto wreckers. I've attached the towbar but I can't find where the wiring harness should plug in. It's supposed to be a plug and play kit but not sure where the plugs are hidden in the boot area.
Any help would be appreciated!
(2012 Lancer sportback)