Voltage Output Test - Mercury MerCruiser MCM 454 Mag MPI Service Manual

CHARGING SYSTEM

Voltage Output Test

Perform this test to determine if voltage regulator is operating correctly, using a 0-20 volt DC
voltmeter.
IMPORTANT: Battery MUST BE fully charged (1.260 or above specific gravity) to
obtain proper voltage reading in this test. If necessary, charge battery with a battery
charger or allow engine to run a sufficient length of time to fully charge battery before
taking reading.
1. Connect positive (+) voltmeter lead to positive battery terminal and negative (–)
voltmeter lead to negative terminal.
2. Start engine and run at fast idle until engine reaches normal operating temperature.
Adjust engine speed to 1500-2000 rpm and observe voltmeter for highest reading.
Reading should be between 13.9 and 14.7 volts.
3. If reading is high, check for a loose or dirty regulator ground lead connection. If connec-
tion is good (and sensing circuit checked out good in "Circuitry Test"), voltage regulator
is faulty and must be replaced. Be sure to disconnect battery cables before attempting
to remove regulator.
Be sure that engine compartment is well-ventilated and that there are no gasoline
vapors present (during the next steps) to prevent the possibility of an explosion
and/or fire, should a spark occur.
DO NOT allow the jumper wire to contact alternator end frame (in next step), as
rectifier and diode assembly may be damaged.
4. Remove four nuts holding excitation and sensing wires and Phillips screw. Remove reg-
ulator cover and install wires and nuts for testing. Connect a jumper wire from the ground
stud to the brush terminal on the lower right- hand side of the brush assembly. Restart
engine and gradually increase engine speed to 1500 rpm while observing voltmeter. DO
NOT allow voltage to exceed 16 volts.
Index
Page 4C-12
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a - Output Wire - ORANGE
b - Excitation Wire - PURPLE
c - Sensing Wire - RED/PURPLE
d - Voltmeter (0-20 Volts)
e - Ground
a
e
c
b
WARNING
CAUTION
SERVICE MANUAL NUMBER 23
d
72788
90-861326--1 MARCH 1999