Do any cars use higher voltage for power distribution to reduce currents and thus reduce the diameter of wire needed? I'm thinking something like having a higher voltage power distribution network that distributes power to nodes that use a DC to DC converter to provide 12 V to the lights, sensors, etc near those nodes.
24v and 36v are common in trucks and industrial vehicles respectively for exactly this reason, among others. It's really expensive to increase voltage though because all the different components' power supplies have to be designed for transients and supply voltages anywhere from 2-5x nominal in normal operation. Companies will often design up to around 200v, for example.
High power systems do exist, particularly in electric vehicles. They have different challenges to do with being incredibly dangerous to work on.
Tesla have been pushing for a standardized 48v supply system for some time for exactly the reason that 12v 15-30A requires much thicker wiring than a 48v 5A system.
