The next major step is to prepare the bundle of wires that connects the front batteries and controls with the rear batteries/controls.
I use my front hallway to measure, cut and line up all the specified wires in the instructions.
Here are all the wires with masking tape holding them together at 12" intervals so they feed through the heater duct more easily.
The instructions call for seven feet of mechanics wire to fish the cable bundle through the heater duct. Being an electrical engineer, I'm not sure what mechanics wire is, so I settled for this soft galvanized steel wire. Here's the loop in the end to prevent the wire from snagging in the duct as I fish it through.
After fishing the wire through, the tail end protrudes from the heater duct in the passenger compartment.
The looped end which I fed through the duct has come out the other end into the engine compartment. It took some patience and some well-placed bends, but the wire slid through reasonably well.
Next up: calling a friend to help me fish the high-current cable bundle through the heater duct.