Sensing Circuit; Current Output Test - MerCruiser GM4 Service Manual

4. If reading is between .75 and 1.1 volts, rotor field
circuit probably is shorted or grounded. Disas-
semble alternator and test rotor as outlined under
"Alternator Repair," following.
5. If reading is between 6.0 and 7.0 volts, rotor field
circuit probably is open. Remove regulator and in-
spect for worn brushes or dirty slip rings. Replace
brushes if less than 1/4 in. (6 mm) long. If brushes
and slip rings are in good condition, disassemble
and perform rotor test as outlined under "Compo-
nent Testing - Rotor" following.
TEST 1
c
a - Excitation Wire - PURPLE
b - Sensing Wire - RED/PURPLE
c - Tie Bar
d - Voltmeter (0-20 Volts)
e - Ground

SENSING CIRCUIT

1. Unplug RED/PURPLE lead from voltage regula-
tor.
2. Connect positive (+) voltmeter lead to RED/PUR-
PLE lead and negative (–) voltmeter lead to
ground terminal.
Index
4C - 6 - CHARGING SYSTEM
TEST 2
d
e
b
a
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3. Voltmeter should indicate battery voltage. If bat-
tery voltage is not present, check sensing circuit
RED/PURPLE lead for loose or dirty connection
or damaged wiring.
b
a - Output Wire - ORANGE
b - Excitation Wire - PURPLE
c - Sensing Wire - RED/PURPLE
d - Voltmeter (0-20 Volts)
e - Ground

Current Output Test

Perform this test to check if alternator is capable of
producing rated current output, using a 0-50 amp DC
ammeter.
! WARNING
Be sure that engine compartment is well-venti-
lated and that there are no gasoline vapors pres-
ent (during the test) to prevent the possibility of
an explosion and/or a fire, should a spark occur.
1. Disconnect negative (–) battery cable from bat-
tery.
2. Disconnect ORANGE lead from alternator output
terminal and connect ammeter in series between
lead and output terminal. Connect positive (+)
side of ammeter toward output terminal.
3. Reconnect negative battery cable.
4. Remove coil wire from distributor cap tower and
ground it to block. Turn on all accessories and
crank engine over with starter motor for 15-20 se-
conds.
d
a
e
c
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90-816462 2-695