See Figures 1, 2, 3, 4 and 5
The alternator charging system is a negative ground system which consists of an alternator, a regulator, a charge indicator, a storage battery and wiring connecting the components, and fuse link wire.
The alternator is belt-driven from the engine. Energy is supplied from the alternator/regulator system to the rotating field through two brushes to two slip-rings. The slip-rings are mounted on the rotor shaft and are connected to the field coil. This energy supplied to the rotating field from the battery is called excitation current and is used to initially energize the field to begin the generation of electricity. Once the alternator starts to generate electricity, the excitation current comes from its own output rather than the battery.
The alternator produces power in the form of alternating current. The alternating current is rectified by 6 diodes into direct current. The direct current is used to charge the battery and power the rest of the electrical system.
When the ignition key is turned on, current flows from the battery, through the charging system indicator light on the instrument panel, to the voltage regulator, and to the alternator. Since the alternator is not producing any current, the alternator warning light comes on. When the engine is started, the alternator begins to produce current and turns the alternator light off. As the alternator turns and produces current, the current is divided in two ways: part to the battery to charge the battery and power the electrical components of the vehicle, and part is returned to the alternator to enable it to increase its output. In this situation, the alternator is receiving current from the battery and from itself. A voltage regulator is wired into the current supply to the alternator to prevent it from receiving too much current which would cause it to put out too much current. Conversely, if the voltage regulator does not allow the alternator to receive enough current, the battery will not be fully
charged and will eventually go dead.
The battery is connected to the alternator at all times, whether the ignition key is turned on or not. If the battery were shorted to ground, the alternator would also be shorted. This would damage the alternator. To prevent this, a fuse link is installed in the wiring between the battery and the alternator. If the battery is shorted, the fuse link is melted, protecting the alternator.
In 1986, the alternators experienced engineering changes, which are: The elimination of the diode trio and the reduction of the external wiring connectors from three-to-two wires.
The new alternators are not serviceable and no periodic maintenance is required.
Observing these precautions will ensure safe handling of the electrical system components and will avoid damage to the vehicle's electrical system:
- Be absolutely sure of the polarity of a booster battery before making connections. Connect the cables positive-to-positive and negative-to-negative. If jump starting, connect the positive cables first and the last connection to a ground on the body of the booster vehicle, so that arcing cannot ignite the hydrogen gas that may have accumulated near the battery. Even a momentary connection of a booster battery with polarity reversed may damage the alternator diodes.
- Disconnect both vehicle battery cables before attempting to charge the battery.
- Never ground the alternator output or battery terminal. Be cautious when using metal tools around a battery to avoid creating a short circuit between the terminals.
- Never run an alternator without a load unless the field circuit (1985) is disconnected.
- Never attempt to polarize an alternator.
- Never disconnect any electrical components with the ignition switch turned ON.
CHARGING SYSTEM TROUBLESHOOTING
See Figures 6 and 7
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.
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 truck.
- 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 truck.
- 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 form 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.
PRELIMINARY CHARGING SYSTEM TESTS
- If you suspect a defect in your charging system, first perform these general checks before going on to more specific tests.
- Check the condition of the alternator belt and tighten it if necessary.
- Clean the battery cable connections at the battery. Make sure the connections between the battery wires and the battery clamps are good. Reconnect the negative terminal only and proceed to the next step.
- With the key off, insert a test light between the positive terminal on the battery and the disconnected positive battery terminal clamp. If the test light comes on, there is a short in the electrical system of the truck. The short must be repaired before proceeding. If the light does not come on, proceed to the next step.
If the truck is equipped with an electric clock, the clock must be disconnected.
- Check the charging system wiring for any obvious breaks or shorts.
- Check the battery to make sure it is fully charged and in good condition.
CHARGING SYSTEM OPERATIONAL TEST
You will need a current indicator to perform this test. If the current indicator is to give an accurate reading, the battery cables must be the same gauge and length as the original equipment.
- With the engine running and all electrical systems turned off, place a current indicator over the positive battery cable.
- If a charge of roughly 5 amps is recorded, the charging system is working. If a draw of about 5 amps is recorded, the system is not working. The needle moves toward the battery when a charge condition is indicated, and away from the battery when a draw condition is indicated.
- If a draw is indicated, proceed with further testing. If an excessive charge (10-15 amps) is indicated, the regulator may be at fault.
- You will need an ammeter for this test.
- Disconnect the battery ground cable.
- Disconnect the wire from the battery terminal on the alternator.
- Connect the ammeter negative lead to the battery terminal wire removed in step three, and connect the ammeter positive lead to the battery terminal on the alternator.
- Reconnect the battery ground cable and turn on all electrical accessories. If the battery is fully charged, disconnect the coil wire and bump the starter a few times to partially discharge it.
- Start the engine and run it until you obtain a maximum current reading on the ammeter.
- If the current is not within 10 amps of the rated output of the alternator, the alternator is working properly. If the current is not within 10 amps, insert a screwdriver in the test hole in the end frame of the alternator and ground the tab in the test hole against the side of the hole.
- If the current is now within 10 amps of the rated output, remove the alternator and have the voltage regulator replaced. If it is still below 10 amps of rated output, have the alternator repaired.
REMOVAL & INSTALLATION
See Figures 8, 9, 10 and 11
The following procedures require the use of GM Belt Tension Gauge No. BT-33-95-ACBN for regular V-belts, or BT-33-97M for serpentine belts. The belt should deflect about 6mm (1/4in.) over a 178-254mm (7-10 in.) span, or 13mm (1/2in.) over a 330-406mm (13-16 in.) span at this point.
- Disconnect the negative battery terminal from the battery.
- Remove the top radiator hose bracket from the radiator.
- Remove the wiring harness that is clamped to the radiator core support.
- Remove the upper fan support-to-radiator support bolts and the fan support.
- Label and disconnect the alternator's electrical connectors.
- Remove the alternator brace bolt and the drive belt.
- Support the alternator, then remove the mounting bolts and the unit from the vehicle.
Install the alternator and adjust the drive belt tension. Torque the top mounting bolt as follows:
2.5L to 20 ft. lbs. (27 Nm)
Lower mounting bolt as follows:
2.5L to 37 ft. lbs. (50 Nm)
- Reconnect the negative battery terminal.
To adjust the drive belt, perform the following procedures:
- If the belt is cold, operate the engine (at idle speed) for 15 minutes; the belt will seat itself in the pulleys allowing the belt fibers to relax or stretch. If the belt is hot, allow it to cool, until it is warm to the touch.A used belt is one that has been rotated at least one complete revolution on the pulleys. This begins the belt seating process and it must never be tensioned to the new belt specifications.
- Loosen the component-to-mounting bracket bolts.
- Using a GM Belt Tension Gauge No. BT-33-95-ACBN (standard V-belts) or BT-33-97M (poly V-belts), place the tension gauge at the center of the belt between the longest span.
- Applying belt tension pressure on the component, adjust the drive belt tension to the correct specifications.
- While holding the correct tension on the component, tighten the component-to-mounting bracket bolt.
- When the belt tension is correct, remove the tension gauge.
See Figures 12, 13, 14, 15, 16, 17, 18 and 19
- Disconnect the negative battery cable.
- Disconnect the terminal plug and battery lead from the alternator.
- Remove the drive belt.
- Remove the alternator brace.
- Remove the mounting bolts.
- Remove the alternator from the alternator mounting bracket.
- Install the alternator in the alternator mounting bracket.
- Install the mounting bolts. Tighten the front mounting bolts to 36 ft. lbs. (50 Nm).
- Install the alternator brace. Tighten the brace to alternator bracket bolt to 36 ft. lbs. (50 Nm).
- Tighten the brace-to-alternator bolt to 18 ft. lbs. (25 Nm).
- Install the drive belt.
- Connect the terminal plug and battery lead to the alternator.
- Connect the negative battery cable.
- Start the engine and check for proper charging system operation.