MerCruiser 305 CID (5.0L) Service Manual page 322

SERVICE MANUAL NUMBER 24
Testing
Charging System
1. Check belt condition and tension.
2. Check battery condition.
3. With a fully charged battery, connect voltmeter leads directly to the battery posts.
4. Start engine and run at 1300-1500 rpm. Read voltmeter. Most systems will read
13.8-14.8 volts.
NOTE: If the voltage reading is within specifications, switch voltmeter to AC volt position.
There should not be more than a 0.250 AC voltage reading with the engine running. A read-
ing more than 0.250 AC volts indicate defective diodes in the alternator.
5. If the voltmeter reading at the battery posts is below 13.5 volts, connect the voltmeter
positive (+) lead to the alternator output terminal. Connect the voltmeter negative (–)
lead to the ground terminal on the alternator. Repeat step 4.
Typical
6. If voltmeter reading is now within specifications, there is too much resistance between
the alternator and the battery.
7. If the reading is below 12.5 volts, the alternator may not be charging. Check all wiring
leading to the alternator.
Index
90-861327--1 OCTOBER 1999
–
76533
a - Output Terminal
b - Ground Terminal
c - Voltmeter
X.X
+
+
c
a
–
b
CHARGING SYSTEM
–
X.X
+
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