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"Wiring harnesses have replaced all the vacuum lines"Of course, now days the wiring harnesses themselves have become huge and unwieldy in many vehicles - literal miles of cables! Automakers are looking at technologies like automotive ethernet and even wireless communication in order to reduce the cost, size and complexity of wiring.
> "I share your attitude WRT modern EVs, but I bet if we just treat the controller and battery as black boxes we don't attempt to disassemble and service"
Some EV batteries are quite serviceable (eg: LEAF), with the pack being able to be disassembled right down to the cell level relatively easily. Although admittedly, some modern pack designs are moving away from this level of serviceability (eg: Tesla, whose cells are cemented in place with fire-retardant foam/glue. Disassembly is a one-way operation).
Things like motor controllers/inverters tend to be very reliable so there is rarely any need to disassemble or service them during the lifetime of the vehicle. If they do fail there's a ready supply of affordable replacement parts, thanks to salvage from crashed vehicles, so it's often easier to just replace a faulty part than attempt to service.