Component Tests and General Diagnostics: Diagnosis and Testing

1. Connect volt/ammeter, and oscilloscope if available, following manufacturer's instructions.
2. Start engine and run until it reaches normal operating temperature.
3. Switch on electrical accessories to create load and maintain engine speed of 900-1000 RPM.
4. Regulated voltage should be within specifications, charge rate should be greater than 15 amperes and scope pattern, if applicable, should show a ripple of less than 6%. Refer to oscilloscope manufacturer's instructions to diagnose variances in scope pattern.
5. If charge indicator lamp goes out while engine is running and scope pattern is acceptable, but regulated voltage is less than specified, or if regulated voltage is greater than specified, check for defective voltage regulator.
6. If voltage or amperage are not as specified, or if charge indicator remains illuminated, check for open or grounded D+ lead.
7. If wiring is satisfactory and charging system malfunction persists, repair or replace alternator as needed.
8. After performing test, turn off accessories and return engine to idle.