Engine Electrical 6D-7
Maintenance
The most common indication of charging system
troubles is an undercharged or overcharged battery.
Since the battery itself may be defective, the first step
should be to check its condition as described under
“Diagnosis of Battery.” In the case of an undercharged
battery, check for battery drain caused by grounds or
by accessories left turned on.
Keep the generator and all other electrical system
terminals clean and tight. A loose or badly corroded
terminal connection will create excessive resistance in
the system and result in hard starting, dim lights etc.
Inspect the generator system at regular intervals and
correct any potential causes of trouble before vehicle
performance is affected.
Diagnosis of Charging System
Trouble in the charging system will be evidenced as
one or more of the following three conditions:
1. The battery discharge warning light will stay on.
2. An undercharged battery as evidenced by slow
cranking.
3. An overcharge, or overvoltage, condition.
Undercharged Battery
Inspection
1. Accessories to be sure none were left on for
extended periods.
2. Drive belt for proper tension. Refer to “Drive Belt”
in Section 6B.
3. The ECM main relay has been ON stuck at the
ignition switch OFF position. (Battery voltage is
consumed.)
4. Battery. Refer to “Diagnosis of Battery” earlier in
this section.
5. Wiring and connections for corrosion or looseness.
Overcharge (or Overvoltage) condition
A charging rate in excess of 29.5-volts for a prolonged
period may cause early electrical system failure.
Blown fuses, light bulbs burned out, and even battery
failure may result. If this condition exists, test the
generator as described under “Generator Output Tests”
later in this section.
Noisy Generator
Inspection
1. Drive pulley for looseness.
2. Mounting bolts for looseness.
3. Bearings for dirt, damage, or wear.
Generator noise may also be caused by worn or
damaged diodes and/or starter.
Electrical Tests
Before performing the following generator electrical
tests on the vehicle, be certain that the system wiring is
not defective and generator belts are not slipping. Also,
the battery must be fully charged for a valid test of the
charging system.
Notice:
To avoid damage to the vehicle electrical system,
always observe the following precautions:
• Do not polarize the generator.
• Do not short across or ground any of the terminals
in the charging circuit except as specifically
instructed herein.
• NEVER operate the generator with the output
terminal open-circuited.
• Be sure the generator and battery have the same
ground polarity.
• When connecting a charger or booster battery to
the vehicle battery, connect negative to negative
and positive to positive.
1. With the engine control switch “ON” and engine not
running, connect a voltmeter from terminal “E” to
ground. The voltmeter should read zero volts.
2. With the engine control switch “ON” and engine not
running, connect a voltmeter from terminal “B” to
ground. The voltmeter should read at least 24
volts.
3. With the engine control switch “ON” and the engine
not running, connect a voltmeter from white wire
side of the connector to ground. The voltmeter
should show 24 volts.
4. With the engine control switch “ON” and the engine
not running, the “charge” light should be on. This
shows that the other circuit in the connection is
working.
5. With the engine running and the headlight high
beams turned on, read the voltage at the “B” post
on the generator. The voltage should be at least 24
volts.
6. If steps 1 through 4 are not OK, check connectors
in the harness for looseness or corrosion and
retest.
7. If step 5 voltage is low, substitute a known good
regulator and test again. If the voltage is still low,
bench test the generator.