Page 281 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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Electrical systems 265

Figure 3.15 Multifunction switch Figure 3.16 Simple ‘cube’ relay

Figure 3.17 Blade fuses

example, a vehicle’s indicators, headlights and horn. These are described as
multifunction switches ( Fig. 3.15 ).
A relay is a very simple device ( Fig. 3.16 ). It can be thought of as a remote-
controlled switch. A very small electric current is used to magnetize a small
winding. The magnetism then causes some contacts to close, which in turn can
control a much heavier current. This allows small, delicate switches to be used,
to control large current users, such as the headlights or the heated rear window.
Some form of circuit protection is required to protect the electrical wiring of
a vehicle and to protect the electrical and electronic components. It is now
common practice to protect almost all electric circuits with a fuse. A fuse is the
weak link in a circuit. If an overload of current occurs then the fuse will melt and
disconnect the circuit before any serious damage is caused. Automobile fuses
are available in three types: glass cartridge, ceramic and blade ( Fig. 3.17 ).
The blade type is now the most popular choice owing to its simple construction
and reliability. Fuses are available in a number of rated values ( Table 3.2 ). Only Key fact
the fuse recommended by the manufacturer should be used. A fuse is used to protect the device
as well as the wiring.
A fuse is used to protect the device as well as the wiring. A good example of this
is a fuse in a wiper motor circuit. If a value were used that was much too high
then it would still protect against a severe short-circuit. However, if the wiper