Routing the loom
The next task is to feed the loom into the interior cabin. There is a rubber grommet behind the battery we can use to do this. You need to access it from both sides. From the engine side, you can move the battery forward and gain just enough access without having to remove the battery. You can remove it if you prefer, it will grant more space to work with, but I didn't want to fuss of removing it and having to reset settings etc on the car. It can be done by just moving it forward while still connected. To move it you need to remove the holding bracket, which is secured with a 13mm bolt:
Pull the battery towards the front of the car as far as it will go.
Now you need to get access from the inside. Start by removing the lower panel in the passenger footwell. It is secured by 3 torx screws:
Then, looking up towards the left, there is some insulation you need to remove. After you will see cables running through the rubber grommet already. This area is confined and hard to work in, so patience is key. Use your hands to feel for the grommet and the existing cables. Once you have found/located it, you need to pass some spare cable/string through it to establish a route. Use a generous amount to work with. I used a stick and taped the spare cable to it. I pushed it through the rubber grommet and into the engine bay. This is the view from behind the battery:
The red thing you can see is the stick poking out of the grommet. This part is also tricky and may take time. When you've got it through, attach the wires from the washer jet loom and pull them into the cabin, then route the remaining cable around the back of the battery, and refit the battery & bracket.