Harness Voltage Test; Open Diode-Trio Test - MerCruiser GM4 Service Manual

2. If voltage output does not fall within specifica-
tions, alternator should be tested for probable
cause and disassembled for repair.
a
a - Output Wire - ORANGE
b - Excitation Wire - PURPLE
c - Sensing Wire - RED/PURPLE
d - Voltmeter (0-20 Volts)
e - Ground

HARNESS VOLTAGE TEST

With ignition off, unplug red/purple wire and check for
battery voltage at harness wire. No voltage at har-
ness wire indicates wiring harness is "open" and
should be repaired or replaced.
c
a - Excitation Wire - PURPLE
b - Sensing Wire - RED/PURPLE
c - Voltmeter (0-20 Volts)
d - Ground
Index
4C - 24 - CHARGING SYSTEM
b
c
d
e
73081
a
b
d
73082

OPEN DIODE-TRIO TEST

1. With ignition on and engine not running, check for
battery voltage at alternator output terminal (Test
1) and 1.5 to 3.0 volts at regulator terminal (Test
2).
a
b
a - Regulator Terminal
b - Output Terminal
c - Ground
d - Voltmeter (0-20 Volts)
2. Connect a jumper wire between regulator and
output terminal. Start engine and run at idle. If
charging voltage (13.8-14.8 volts) is present at
output terminal, the diode-trio is probably defec-
tive and alternator should be removed for repair.
a
b
c
a - Regulator Terminal
b - Output Terminal
c - Jumper Lead
d - Ground
e - Voltmeter (0-20 Volts)
c
d
73083
d
e
73084
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