maybe i missed in your estimate, but most circuits need more than one wire?
hn72774
In a vehicle, the chassis is the negative wire in the circuit.
AlotOfReading
The vast majority of automotive buses use differential signaling over multiple conductors for EMI reasons. The only common exception is LIN and maybe SWCAN if we're exceedingly generous with our definition of "common".
caleblloyd
I didn’t completely follow either but I think the n^2 = 400 worked out to 20 ECUs each with 20 wires