Systematic diagnostic testing of the charging system components including alternator output, voltage regulator function, and battery condition to verify proper electrical system operation.

Warnings

Tools required

Parts

• Battery terminal protectant spray × 1 — Use any dielectric grease or terminal spray

Preparation

1. Park vehicle on level surface and apply parking brake
2. Turn off all electrical accessories including headlights, radio, heater blower, and wipers
3. Allow engine to cool if recently operated
4. Clean battery terminals and cable connections of any corrosion
5. Verify battery electrolyte levels are correct (if not maintenance-free battery)
6. Ensure alternator drive belt is present and properly tensioned

Procedure

1. 1

   Perform visual inspection of charging system
   Inspect the alternator mounting bolts for tightness. Check the drive belt for proper tension (should deflect 1/2 inch under moderate thumb pressure at mid-span), cracks, or glazing. Examine all visible wiring connections to the alternator, voltage regulator (externally mounted on firewall), and battery for damage, corrosion, or looseness. Check battery case for cracks or bulging.
2. 2

   Test battery state of charge
   Using a digital multimeter, measure battery voltage with engine off and all accessories off. A fully charged battery should read 12.6 volts or higher. Readings of 12.4 volts indicate 75% charge, 12.2 volts indicate 50% charge, and below 12.0 volts indicate a discharged battery requiring charging before further testing. Record this voltage for comparison.
3. 3

   Test charging system output voltage
   Connect voltmeter across battery terminals. Start the engine and allow it to idle. The voltage should rise to 13.8-14.8 volts, indicating the alternator is charging. If voltage remains below 13.5 volts or exceeds 15.0 volts, there is a charging system problem requiring further diagnosis.
4. 4

   Perform loaded output test
   With engine running at approximately 1500-2000 RPM and voltmeter still connected, turn on high-beam headlights and heater blower on high speed. Voltage should remain above 13.5 volts. If voltage drops below 13.0 volts under load, the alternator may not be producing adequate amperage or the voltage regulator may be faulty.
5. 5

   Check alternator field circuit
   Locate the two-wire connector at the alternator. The blue wire provides field excitation from the ignition switch through the voltage regulator. With ignition on and engine off, check for battery voltage at this wire. No voltage indicates a problem in the field circuit or voltage regulator. The black wire is the field ground and should show continuity to ground.
6. 6

   Test voltage regulator operation
   The 1970 Rebel Machine uses an external electromechanical voltage regulator mounted on the firewall. With engine running at fast idle (1500 RPM), voltage at battery should stabilize between 13.8-14.8 volts. Tap the voltage regulator case lightly with a screwdriver handle while observing the voltmeter. Erratic voltage readings indicate failing regulator contacts requiring replacement.
7. 7

   Inspect alternator output wire and connections
   Locate the large red output wire connected to the alternator output terminal (marked BAT or +). Check this connection for tightness and corrosion. Trace this wire to the starter solenoid junction where it connects to the battery positive circuit. Any loose connections or corroded terminals in this circuit will cause voltage drop and apparent charging problems.
8. 8

   Verify alternator ground circuit
   The alternator must have a solid ground path through its mounting bracket to the engine block. Using an ohmmeter with engine off, measure resistance between alternator case and battery negative terminal. Resistance should be less than 0.5 ohms. Higher resistance indicates poor grounding, which can cause reduced output or erratic operation.
9. 9

   Check for parasitic draw
   With engine off and all accessories off, disconnect the negative battery cable and connect an ammeter in series between the cable and battery post. Normal draw should be near zero (less than 50 milliamps) on this vintage vehicle. Higher draw indicates a short circuit or component drawing power when it should be off, which can discharge the battery and appear as a charging problem.

Reassembly

1. Reconnect any test equipment and restore all connections to original condition
2. Apply terminal protectant to battery connections to prevent future corrosion
3. Ensure all electrical connectors are fully seated and secured

Verification

• Start engine and verify voltage reads 13.8-14.8 volts at idle with no accessories on
• Turn on headlights and heater blower; voltage should remain above 13.5 volts at 1500 RPM
• Test drive vehicle and verify charging system warning light (if equipped) remains off during operation
• Allow engine to idle for 5 minutes and recheck voltage to ensure regulator maintains proper voltage without overcharging

More procedures for this vehicle