Circuitry Test - Mercury MerCruiser MCM 454 Mag MPI Service Manual

SERVICE MANUAL NUMBER 23

Circuitry Test

Perform the following tests, using a 0-20 volt DC voltmeter, to check that all of the circuits
between the alternator and the other components within the alternator system are in good
condition.
OUTPUT CIRCUIT
1. Connect positive (+) voltmeter lead to alternator output terminal and negative (–) lead
2. Wiggle engine wiring harness while observing voltmeter. Meter should indicate approxi-
EXCITATION CIRCUIT
1. Connect positive (+) voltmeter lead to tie strap terminal on alternator and negative (–)
2. Turn ignition switch to ON position and note voltmeter reading. Reading should be 1.3
3. If no reading is obtained, an opening exists in alternator excitation lead or in excitation
4. If reading is between .75 and 1.1 volts, rotor field circuit probably is shorted or grounded.
Index
90-861326--1 MARCH 1999
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to a ground terminal on alternator.
mate battery voltage and should not vary. If no reading is obtained, or if reading varies,
check alternator output circuit for loose or dirty connections or damaged wiring.
a - Output Wire - ORANGE
b - Excitation Wire - PURPLE
c - Sensing Wire - RED/PURPLE
d - Voltmeter (0-20 Volts)
e - Ground
lead to a ground terminal on alternator (Test 1).
to 2.5 volts.
circuit of regulator. Unplug PURPLE lead from regulator. Connect positive voltmeter
lead to PURPLE lead and negative voltmeter leads to ground (Test 2). If voltmeter now
indicates approximate battery voltage, voltage regulator is defective and must be
replaced. If no voltage is indicated, check excitation circuit for loose or dirty connections
or damaged wiring.
Disassemble alternator and test rotor as outlined under "Alternator Repair," following.
d
a
e
c
b
CHARGING SYSTEM
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