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ELECTRICAL
236
CHECKING FUSES:
If any electrical unit in the vehicle has
stopped functioning, fuses should be checked first.
A blade type fuse has test taps provided to
allow checking of the fuse itself without removing it
from the fuse block. The fuse is okay if the test
light comes on when its one lead is connected to
the test taps (
one at a time
) and the other lead of
the test light is grounded. Remember to turn the
ignition switch to ON to ensure all circuits are live.
CAUTIONS IN EVENT OF BLOWN FUSE
When a fuse is blown, there are two
probable causes. One is that it is blown due to flow
of current exceeding its rating. The other is that it
is blown due to repeated on/off current flowing
through it. Which of these two causes were
responsible for the fuse to be blown can be
determined by visual check as described below.
1. Fuse blown due to current exceeding rating
The illustration shows the state of a fuse
blown due to this cause. In this case, do not
replace the fuse with a new one quickly since a
current heavy enough to blow the fuse has flowed
through it. First, check the circuit for shorts and
check for abnormal electric parts. After correcting
shorts or replacing parts, use only a fuse of the
same capacity as a replacement. Never use a fuse
of larger capacity than the original fuse. If a larger
capacity fuse is used, electric parts or wiring could
be damaged, or could start a fire.
2. Fuse blown due to repeated turning current on
and off:
The illustration shows the state of a fuse
blown due to repeated current on/off. Normally,
this type of problem occurs after a fairly long
period of use and is less frequent than above. In
this case, simply replace with a new fuse of the
same capacity.
CHECKING RELAYS:
1.
By using a relay, a heavy current can be turned
on and off by a switch using much less current.
For example, in the circuit shown here, when the
switch is turned on (
closed
), current flows to the
coil of the relay. Then, its contact is turned on
(
closed
) and the light comes on. The current
flowing through the switch is much less than that
for the light.
2. Relays may be classified as the normally open-
type or the normally closed-type, depending on
their contact construction.
NOTE:
The De-energized state means that no
current is flowing through the coil. The energized
state means that current is flowing through the
coil.
(a)The normally open-type
When a normally open relay as illustrated here
is checked, there should be no continuity
between terminals 30 and 87 when the relay is
de-energized. There should be continuity
between terminals 30 and 87 when battery
voltage and ground are applied to terminals 85
and 86. The relay condition is determined by
this check.
NOTE:
Check the relay in both condition, i.e.
energized and not energized