B
60
Repair and Service Manual
ELECTRICAL SYSTEM
Read all of SAFETY and this section before attempting any procedure. Pay particular attention to Notices, Cautions, Warnings and Dangers.
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FAULT DIAGNOSIS
General
In order to effectively fault diagnose the circuits that
include the horn, lighting, brake/turn signals and gauges,
the technician must be able to use the wiring diagram and
a DVOM.
The wiring diagram shows the path followed by a voltage
or signal from its origination point to its destination. Each
wire is indicated by color.
The technician should use simple logic fault diagnosing in
order to reduce the number of steps required to isolate
the problem.
Example 1:
If the vehicle will not start and none of the
lights function (or burn dimly) the battery should be tested
before trying to fault diagnose the lighting circuit.
Example 2:
If a problem occurs in the lighting circuit that
results in only one of the headlights not working, there is
no reason to check battery wiring or the fuse since it is
obvious that voltage is present. Since bulbs will burn out
over time, the obvious place to start is at the headlight
that is not functioning. If power is present at the connector
and the ground wiring is satisfactory, the only possibilities
that exist are a burned out bulb or a poor contact between
the connectors and the headlight.
If power is not present but the other headlight functions, a
wiring problem is indicated between the two headlights.
In some cases where battery voltage is expected, the
easiest way to test the circuit is to set the DVOM to DC
volts and place the negative (-) probe of the DVOM on the
negative battery terminal. Move the positive (+) probe to
each wire termination starting at the battery and working
out to the device that is not working. Be sure to check
both sides of all switches and fuses.
When no battery voltage is found, the problem lies
between the point where no voltage is detected and the
last place that voltage was detected. In circuits where no
voltage is expected, the same procedure may be used
except that the DVOM is set to continuity. Place the nega-
tive (-) probe on a wire terminal at the beginning of the cir-
cuit and work towards the device that is not working with
the positive (+) probe. When continuity is no longer indi-
cated, a failed conductor or device is indicated.
Testing Battery Voltage
It is important to determine the condition of the battery set
before proceeding with any electrical fault diagnosing. An
open voltage test is of little use since a battery that has
deteriorated to the point of needing replacement can still
show eight volts or higher in an open voltage test. If there
is any doubt as to the adequacy of the battery set, charge
the batteries and perform a load test using a discharge
machine following manufacturer’s instructions. If batteries
are satisfactory, recharge battery set.
With the adequacy of the batteries confirmed, use a
DVOM connected directly to the battery terminal posts to
determine the open voltage of the set. In the following
tests, this voltage level will be used as a reference. Some
loss due to resistance of wires and connectors may be
indicated by readings that could be up to one volt less
than the reference voltage. No reading indicates an
“open” condition and the battery wires should be
inspected for a broken or disconnected wire or compo-
nent.
Continuity Check
To prevent possible injury or death resulting
from a battery explosion, use an insulated
wrench and remove the BL- wire from the bat-
tery to disconnect electrical power to vehicle.
Turn the key switch to ‘OFF’ and place the direction
selector in neutral before disconnecting power by remov-
ing the BL- connection to the battery. Always use insu-
lated wrenches when working on batteries. To check for
continuity, set the DVOM to the K
Ω
setting and select
‘Continuity’. The meter will give an audible signal when it
detects continuity. If the meter does not have a continuity
setting, set it to K
Ω
, the meter will indicate “0” when it
detects continuity.
