1-9. BATTERIES. Batteries are perishable devices
that wear out at some point in time. With use they
deteriorate and eventually become incapable of
performing their important job. In addition, new, good
batteries may become discharged for various reasons.
Neither worn out nor discharged batteries can supply
the power necessary for cranking. Thus the battery
check becomes the starting point for diagnosing
electrical system problems.
1-10. SUB-CIRCUITS. (See Figure 1-1) Because
of vibration, corrosion, temperature changes or damage,
the performance of wiring, connections, and secondary
components as well as the function of the starter and
alternator can deteriorate. This in turn can cause
malfunctions within the starting and charging systems.
For the purpose of testing, wiring and components are
broken down into four circuits that must be tested.
These are:
1. Cranking Circuit. This consists of the large
cables that carry the high starter current. Excessive
loss here causes slow cranking speeds, especially in cold
weather. Inability to start from slow cranking can lead
to starter burn-up if the starter is cranked over 30
seconds. Deeply discharged or worn-out batteries can
also cause the same problem.
2. Solenoid Circuit. This consists of the wiring
from the battery, through a push button or magnetic
switch, to the “S” terminal of the starter solenoid, and
back to the battery. Excessive loss here can cause the
solenoid to shift in and out (chatter) resulting in a no-
start condition. This can cause a burned contact disc
and terminals of the starter solenoid. Deeply discharged
batteries can also cause this problem.
3. Magnetic Switch Circuit (When Magnetic
Switch Used). This is made up of the wiring from the
battery through a key switch and/or start button to
the coil of the magnetic switch and back to the battery.
Excessive loss here can cause a “no start” complaint.
4. Charging Circuit. This consists of the wiring
between the alternator and the battery and back to
the alternator. Excessive loss here can cause the
batteries to not charge properly. As noted above,
discharged batteries will cause other problems.
1-11. SEQUENCE OF PROCEDURES. It is important
that the procedures in the manual be followed in the
exact sequence specified. Batteries, wiring and connec-
tions should be checked and corrected to the specifica-
tions given. If cranking problems still occur, then connect-
ing cables should be checked before replacing the starter
with a known good unit. Similarly, in the charging circuit,
batteries wiring and connections should be thoroughly
checked and corrected to the specifications given. Only
then should the alternator be checked and replaced if
necessary.
1-12. ELECTRICAL FUNDAMENTALS
1-13. TERMS AND DEFINITIONS. Following are
some electrical terms that we will be dealing with in
this manual and their definitions:
1. Voltage (See Figure 1-2). Voltage is the electrical
pressure or force that causes current or electrons to flow
through a conductor. The voltage can also be described as
the difference in electrical pressure between two points
in a circuit. This electrical force or pressure is measured
in volts.
2. Current (See Figure 1-3). Electrical current is the
flow or movement of electrons in a conductor. This move-
ment can be compared to the flow of water through a
pipe. Without pressure (voltage) the current will not flow.
Electrical flow is measured in amperes, most often abbre-
viated as amps.
1-2
VOLTAGE = ELECTRICAL PRESSURE
Figure 1-2. Voltage
DP-1002
Figure 1-4. Resistance
RESISTANCE
(OHMS)
CURRENT
DP-1004
Figure 1-3. Current
FLOW - ELECTRON CURRENT
DP-1003
new diagnostic manual 4/5/05 9:47 AM Page 1-2
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