Printed circuits are plastic sheets on which copper tracks have been printed. Components are plugged directly into the tracks. A few modern cars have flexible printed circuits. The copper tracks are printed in ribbons of flexible plastic, which replace the whole wiring system.
A circuit usually includes more than one component, such as bulbs in the lighting circuits. It matters whether they are connected in series one after the other or in parallel side by side.
Some ancillary components can be operated without the ignition turned on by turning the switch to the auxiliary position. A radio is usually wired through this switch, so that it can be played with the engine off.
Where wires run side-by-side they are bound together in a bundle, in a plastic or fabric sheath, to keep them tidy and less difficult to fit. This bundle of wires stretches over the length of the car, with single wires or small groups of wires emerging where necessary, and is called the wiring loom.