Some components must be connected in series. For example, the sender in the fuel tank varies its resistance according to the amount of fuel in the tank, and sends a small electrical current to the fuel gauge.
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.
Most car handbooks and service manuals include a wiring diagram which can be difficult to follow. The colour-coding, however, is a useful guide to tracing wiring.
The sudden surge of high current in a short circuit makes the fuse wire melt, or blow, breaking the circuit. When this happens, see if there is a short circuit or a disconnection, then install a new fuse of the correct amperage rating (See Checking and replacing fuses).