Could the community help by supplying a relevant manual for a vehicle power system? Any vehicle, could be any make or model of car. It should show the power supply available to the accessories, such as on-board computer, during states such as car off, brake pedal depressed, key in ignition, starting car, driving, and so on.
This patent application uses characteristics of a vehicle power supply to decide when to download software updates to the on-board computer. The power supply conditions are illustrated in figure 3 and other figures.