5-9
DIAGNOSTICS/TROUBLESHOOTING
GENERAL
The TROUBLESHOOTING table, starting on page 5-5, con-
tains detailed procedures to solve and correct problems. Fol-
low the ELECTRIC STARTING SYSTEM DIAGNOSIS
diagram on page 5-7 to diagnose starting system problems.
The VOLTAGE DROPS procedure below will help you to
locate poor connections or components with excessive volt-
age drops.
VOLTAGE DROPS
Check the integrity of all wiring, switches, circuit breakers and
connectors between the source and destination.
The voltage drop test measures the difference in potential or
the actual voltage dropped between the source and destina-
tion.
1. See ITEM A in Figure 5-4. Attach your red meter lead to
the most positive part of the circuit, which in this case
would be the positive post of the battery.
2. See ITEM B in Figure 5-4. Attach the black meter lead to
the final destination or component in the circuit (solenoid
terminal from relay).
3. Activate the starter and observe the meter reading. The
meter will read the voltage dropped or the difference in
potential between the source and destination.
4. An ideal circuit’s voltage drop would be 0 volts or no volt-
age dropped, meaning no difference in potential.
5. See ITEM C in Figure 5-4. An open circuit should read 12
volts, displaying all the voltage dropped, and the entire
difference in potential displayed on the meter.
6. Typically, a good circuit will drop less than 1 volt.
7. If the voltage drop is greater, back track through the con-
nections until the source of the potential difference is
found.
The benefit of doing it this way is speed.
a. Readings aren’t as sensitive to real battery voltage.
b. Readings show the actual voltage dropped, not just
the presence of voltage.
c. This tests the system as it is actually being used. It
is more accurate and will display hard to find poor
connections.
d. This approach can be used on lighting circuits, igni-
tion circuits, etc. Start from most positive and go to
most negative (the destination or component).
8. See ITEM D in Figure 5-4. The negative or ground circuit
can be checked as well. Place the negative lead on the
most negative part of the circuit (or the negative battery
post). Remember, there is nothing more negative than
the negative post of the battery. Place the positive lead to
the ground you wish to check.
9. Activate the circuit. This will allow you to read the poten-
tial difference or voltage dropped on the negative or
ground circuit. This is very effective for identifying poor
grounds due to powdered paint. Even the slightest con-
nection may cause an ohmmeter to give a good reading.
However, when sufficient current is passed through, the
resistance caused by the powdered paint will cause a
voltage drop, or potential difference in the ground circuit.
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