At the turn of the century (1900), when the automobile was first coming of age, electricity was also in its infancy. Many scientist believed electricity flowed from positive to negative (Hole Theory), they didn't know about electrons as yet. During the creation of the nuclear reaction and during the development of the electronic computer in the late 30's and early 40's, the atomic theory was realized. That theory required us to follow the electrons as the only way the electronic computer would operate. That's when they came up with electronic theory and hole theory. It took about ten years to filter down to automobile production for the switch to negative ground instead of positive ground. At the same time as the automobile advanced, more electronics were being installed that needed more electricity at a higher pressure, so when they changed from positive to negative ground, they also upped the voltage to 12 volts.
Now they want to increase the voltage to 42 volts as more and more accessories have been put on vehicles all controlled and/or monitored by computers. However, they can't get the accessories to live any reasonable length of time with that kind of voltage. The 42 volt system is actually a 36 volt system, they just changed how it is promoted. 6v systems are actually have a 7 volt charging system, a 12v system actually has a 14 v charging system and a 36 v system has a 42 volt charging system!
