Troubleshooting Tests (Alternator On Engine); Circuitry Test - Mercury 305 CID Service Manual

Troubleshooting Tests
(Alternator on Engine)
Use the following tests in conjunction with the "Trou-
bleshooting" in Section 1. Before proceeding with the
tests, however, perform the following checks to elimi-
nate possible problem areas. Also observe "Precau-
tions," preceding, to prevent damage to alternator
system.
1. If problem is an undercharged battery, check to
ensure that undercharged condition has not been
caused by excessive accessory current draw or
by accessories which have accidentally been left
on. Also, check that undercharged condition has
not been caused by running engine at too low a
speed for extended periods of time.
2. Check physical condition and state of charge of
battery, as outlined in "Battery - Storage" in Sec-
tion 4A. Battery MUST BE at least 75% (1.230
specific gravity) of fully charged to obtain valid re-
sults in the following tests. If not, charge battery
before testing system.
3. Inspect entire alternator system wiring for de-
fects. Check all connections for tightness and
cleanliness, particularly battery cable clamps
and battery terminals.
4. Check alternator drive belt for excessive wear,
cracks, fraying and glazed surfaces and replace
if necessary. Also, check drive belt tension and
adjust if necessary, as outlined under "Drive Belt
Tension Adjustment."

Circuitry Test

Perform the following tests, using a 0-20 volt DC volt-
meter, to check that all of the circuits between the al-
ternator and the other components within the alterna-
tor system are in good condition.
OUTPUT CIRCUIT
1. Connect positive (+) voltmeter lead to alternator
output terminal and negative (–) lead to a ground
terminal on alternator.
Index
90-823225--1 1096
2. Wiggle engine wiring harness while observing
voltmeter. Meter should indicate approximate
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.
b
a - Output Wire - ORANGE
b - Excitation Wire - PURPLE
c - Sensing Wire - RED/PURPLE
d - Voltmeter (0-20 Volts)
e - Ground
EXCITATION CIRCUIT
1. Connect positive (+) voltmeter lead to tie strap
terminal on alternator and negative (–) lead to a
ground terminal on alternator (Test 1).
2. Turn ignition switch to ON position and note volt-
meter reading. Reading should be 1.3 to 2.5
volts.
3. If no reading is obtained, an opening exists in al-
ternator excitation lead or in excitation 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 ex-
citation circuit for loose or dirty connections or
damaged wiring.
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.
d
a
e
c
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CHARGING SYSTEM - 4C-5