ElectroAuto has you measure two 2/0 welding cable, plus a 10 ga ground wire and a 4-conductor signal cable, then tape everything together at the proper offsets.
The instructions provided a convoluted set of steps using "mechanic's wire" to prep for pulling the cabling through the heater duct, and you need an assistant to do the cable pull. I decided to use my fishtape, and it was easy to do by myself. Here you see the fishtape running into the heater duct from the rear of the car to the front.
The tip of the fishtape sticks up out of the hole just below the fuse block.
I put the end of the fishtape through the lug hold, then strapped it into place with a ziptie.
I then wrapped it in tape to make for a smooth pull.
At the end of the pull, you want a tape marker to just be coming out of the heater tube in the engine compartment.
And this is the other end, with the cable waiting to be bolted to the circuit breaker. I'll have to do some minor pull adjustments to get enough cable.
After finishing the prep, I put the "CA Plug" in place, and used the same silicon as for the saddlebag battery rack. The CA Plug is slightly angled so it didn't want to stay in place. I helped it by sticking a screwdriver in as a wedge.
One small complication due to my use of the weatherproof enclosure. The end of this cable bolts to the contactor but the lug is about 1/16" too wide to get through the weatherproof gland nut. My solution was to grind just enough off to get it to fit through. Unfortunately I forgot to do the grinding before I pulled the cable, so the grinding occurred on the ground under the back of the car.
Final connections on each end happen in later steps.