Relays and control circuits

The Fiesta is equipped with a number of consumers that consume a higher current than other consumers. In order to ensure maximum safety, taking into account the smallest possible cross-sections of wires, these consumers are supplied via separate relays. When using a relay, the switch switches only minor currents to turn on the relay in relation to the current necessary to turn on the consumer itself.

Relay operation

A simple relay is used to control an electrical consumer with a large current consumption. If voltage is applied to such a consumer through long electrical circuits, the voltage will drop sharply. In addition, the switch contacts must switch large currents. When the corresponding consumer is turned on, the electrical circuit of the switch closes and supplies voltage to the relay coil. Under the action of voltage, the relay coil, overcoming the force of the spring, attracts the plate, which closes the relay contacts and turns on the consumer's electrical circuit. The electrical circuit of the consumer reduces the voltage drop, as it runs along a short path, connecting directly through the relay contacts to the consumer.

Relay location

Pic. 15.41. Location of the relay on the reverse side of the fuse and relay box under the instrument panel




Pic. 15.44. Location of the relay in the fuse and relay box in the engine compartment





In the Fiesta, most of the relays are assembled into blocks and mounted on special circuit boards (pic. 15.41, 15.44, tab. 15.5, 15.7). The on-board network also provides additional relays that are located next to the consumer and perform certain functions. These include the turn signal relay, the wiper relay and the pre-heating relay for the diesel engine.