We now sucessfully have tried the Dallas 1-wire bus via a USB-adapter (ds9490R). The bus is hotpluggable so one can add and remove components and detect what is connected. Each component has a unique ID-number so everything can be identified. We will use this system to detect what power plants and factories that are connected.
One cannot detect where something is connected though, but we will solve that by dividing the bus into several spokes that can be connected and disconnected by means of a DS2408 that is a 8 port I/O port that drives 6 reed relays (will post a schematic for that later, but the basics is described here - see the switched network section). This way one can loop through the spokes and detect what is connected to each of them.
A new schematic for the powerplants and factories is displayed here. The IC DS2408 drives 5 LEDs and reads if the GRID-pin is connected to Vcc - in the game this is equivalent to connecting the power plant/factory to the main power grid, thereby getting or using power.
(The cities are actually wired the same way, they just don't have a plug, they are hard wired.)