Service manual
ALTERNATOR
TESTING
e. Now check the voltage between the alternator output
terminal (B+) and ground.
If
the circuit is good, the
voltage at the alternator should be the same as the
bat-
tery, or
if
an isolator is in the circuit the alternator volt-
age will be zero.
If
not, a problem exists in the circuit
between the alternator
and
the battery. Check all the
connections - look for an opening in the charging
cir-
cuit
STARTING
BAmRY
ALTERNATOR
TESTING
11IE
STARTING
BATTERY
•
ALTERNATOR
(ENGINE
RUNNING}
MULTIMETER
..c::~--1
ENGINE
GROUND
£ Start the engine again. Check the voltage between the
alternator output and ground.
The voltage reading for a properly operating alternator
should be between 13.5 and 14.5 volts.
If
your alterna-
tor is over-
or
under-charging, have it repaired at a reli-
able service shop.
NOTE:
Before
removing
the alternator for
repair,
use
a voltmeter
to
ensure
that
12
volts DC excitation is
present
at
the
EXC terminal
if
the
previous test
showed only battery voltage
at
the
B output
terminal.
If
12
volts
are
not present at
the
EXC
terminal,
trace
the
wiring
looking
for breaks
and
poor connections.
Alternator
is
Working
4. Check the voltage
of
the service battery. This battery
should have a voltage between
13
and
14
volts when the
engine is running.
If
not, there is a problem in the service
battery charging circuit. Troubleshoot the service
ba~ery
chargina circuit by checking the wiring and connections,
the
sole~oid,
isolator, battery switch and the battery itself.
MULTIMETER
CKQ)
0
COM
SERVICE
BAmRY
TESnNG
THE
SERVICE
BATTERY
(ENGINE
RUNNING)
A
CAUTION:
When
perfonning
tests
on
the
altemator
charging
circuit
do
not
use
a
high
voltage
tester
(i.e.
Megger}.
You
can
damage
the
alternator
diodes.
ALTERNATOR
INSPECTION
When
rebuilding the engine. The alternator should be cleaned
and inspected. The housing can
be
wiped off with a solvent
and the alternator terminal studs should be cleaned with a
wire brush. Make certain those studs are tight. Also clean the
wiring connections that connect
to
the wiring harness.
Tum
the rotor pulley by hand. It should tum smoothly.
Depending on when the alternator was last serviced, the
brushes
may
need replacing.
If
the alternator is at all suspect,
send
it
to a service shop for testing and overhaul.
38