TIAGO

ELECTRICAL

196

8.27 FUSE AND RELAY BOX DETAILS

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:

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.

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