Conceptually simple, challenging dexterity. In the background you can make out a booted white cable heading down and to the left. That’s the 12V from the starter relay to the starter motor. In the foreground is the ground from the starter to the airframe/battery. Please note that this is the best possible view I could arrange with my camera. Think about trying to squeeze my fat fingers and tools into that space. Miracle, eh?
Starter Motor Wiring