There are many possible ways in which the charging system can malfunction.
Often the source of a problem is difficult to diagnose, requiring special equipment
and a good deal of experience. This is usually not the case, however, where
the charging system fails completely and causes the dash board warning light
to come on or the battery to become dead. To troubleshoot a complete system
failure only two pieces of equipment are needed: a test light, to determine
that current is reaching a certain point; and a current indicator (ammeter),
to determine the direction of the current flow and its measurement in amps.
This test works under three assumptions:
- The battery is known to be good and fully charged.
- The alternator belt is in good condition and adjusted to the proper tension.
- All connections in the system are clean and tight.
NOTE: In order for the current indicator to give a valid
reading, the truck must be equipped with battery cables which are of the
same gauge size and quality as original equipment battery cables.
- Turn off all electrical components on the car. Make sure the doors of the
truck are closed. If the truck is equipped with a clock, disconnect the clock
by removing the lead wire from the rear of the clock. Disconnect the positive
battery cable from the battery and connect the ground wire on a test light
to the disconnected positive battery cable. Touch the probe end of the test
light to the positive battery post. The test light should not light. If the
test light does light, there is a short or open circuit on the car.
- Disconnect the voltage regulator wiring harness connector at the voltage
regulator. Turn on the ignition key. Connect the wire on a test light to a
good ground (engine bolt). Touch the probe end of a test light to the ignition
wire connector into the voltage regulator wiring connector. This wire corresponds
to the I terminal on the regulator. If the test light goes
on, the charging system warning light circuit is complete. If the test light
does not come on and the warning light on the instrument panel is on, either
the resistor wire, which is parallel with the warning light, or the wiring
to the voltage regulator, is defective. If the test light does not come on
and the warning light is not on, either the bulb is defective or the power
supply wire from the battery through the ignition switch to the bulb has an
open circuit. Connect the wiring harness to the regulator.
- Examine the fuse link wire in the wiring harness from the starter relay
to the alternator. If the insulation on the wire is cracked or split, the
fuse link may be melted. Connect a test light to the fuse link by attaching
the ground wire on the test light to an engine bolt and touching the probe
end of the light to the bottom of the fuse link wire where it splices into
the alternator output wire. If the bulb in the test light does not light,
the fuse link is melted.
- Start the engine and place a current indicator on the positive battery cable.
Turn off all electrical accessories and make sure the doors are closed. If
the charging system is working properly, the gauge will show a draw of less
than 5 amps. If the system is not working properly, the gauge will show a
draw of more than 5 amps. A charge moves the needle toward the battery, a
draw moves the needle away from the battery. Turn the engine off.
- Disconnect the wiring harness from the voltage regulator at the regulator
at the regulator connector. Connect a male spade terminal (solderless connector)
to each end of a jumper wire. Insert one end of the wire into the wiring harness
connector which corresponds to the A terminal on the regulator.
Insert the other end of the wire into the wiring harness connector which corresponds
to the F terminal on the regulator. Position the connector
with the jumper wire installed so that it cannot contact any metal surface
under the hood. Position a current indicator gauge on the positive battery
cable. Have an assistant start the engine. Observe the reading on the current
indicator. Have your assistant slowly raise the speed of the engine to about
2,000 rpm or until the current indicator needle stops moving, whichever comes
first. Do not run the engine for more than a short period of time in this
condition. If the wiring harness connector or jumper wire becomes excessively
hot during this test, turn off the engine and check for a grounded wire in
the regulator wiring harness. If the current indicator shows a charge of about
three amps less than the output of the alternator, the alternator is working
properly. If the previous tests showed a draw, the voltage regulator is defective.
If the gauge does not show the proper charging rate, the alternator is defective.
