The wiring among the various "computer modules" (ABS, Air bags, Instrument Cluster, Body computer, Engine computer, Trans controller, etc.) in the vehicle can be done via a network--each module can be programmed to share a remarkably compact wiring harness, to accept or reject certain information sent by other "modules", and to prioritize messages that would otherwise be sent at the same time.
By the time the wire harness gets to individual devices--light bulbs, for example--it works the way it always has. If it has power, the light is on. If the power is shut off, the light is out. And if the power is intermittent, at high frequency, the light is on at partial-brightness.