Symptom Related Diagnostic Procedures

ALTERNATOR WARNING LIGHT TEST

Charging system trouble is indicated by an illuminated alternator warning light on the instrument panel, or by an under or over charged battery.

DESCRIPTION
The alternator generates electrical current by electrical induction.
A magnetic field is placed in motion to induce an electrical current in a stationary coil.
When the engine is running and the alternator is spinning, part of the current it is producing is used to energize its electromagnetic field.
When starting, some other current must be provided to initially energize the field and begin the current generating process.
This current is provided by the battery.
The current to the alternator is routed through the alternator warning light in the instrument cluster.
As soon as the alternator output equals the battery's voltage, the light goes off.
Normally the warning light should be off when the ignition is off and the engine is stopped.
The light should only come on when the ignition is turned on (current to the rotor) and go out again when the engine is started and the battery is being charged.


SYMPTOM
Ignition off, engine not running, and light glowing or on.


TEST INDICATIONS CAUSE/ACTION

Disconnect plug from alternator. Light goes out. Faulty diode/Repair or
replace alternator.


Light does not go out. Short in wiring or
harness/Repair or
replace wiring or
harness.




SYMPTOM
Ignition on, engine not running, light off.

TEST INDICATIONS CAUSE/ACTION
N/A Battery discharged Charge battery.




Remove and test warning N/A Replace if burned out.
light bulb.







If bulb not burned, disconnect plug No voltage Open circuit between
from alternator. Check for voltage plug and battery
between the red wire and ground positive terminal
using a volt meter. /repair wire or
connection.







If voltage is there, keep plug Light does not Faulty bulb socket,
disconnected and ground the come on open circuit in
blue wire to engine. blue wire, or open
circuit between
socket and terminal
15 on ignition switch
/Replace socket. Repair
wires or connection.




Light comes on. Loose connection
between regulator
and alternator
or loose connection
between brushes
and regulator/
Correct loose
connections







Light comes on. Regulator properly
connected. Internal
alternator or
regulator faults/
Repair or replace.




SYMPTOM
Engine running at any speed and light stays on.

TEST INDICATIONS CAUSE/ACTION
N/A Loose or broken Replace or
alternator belt. adjust belt.


Exciter diodes Repair or replace
burned out alternator


Faulty regulator Test charging system
or alternator and repair or
windings replace as needed




High voltage between Repair wires.
positive battery
terminal and
alternator due
to broken,
loose or
corroded wires