If the lamp still does not light, check the electrical circuit from the generator to the lamp.
If all electrical circuits are working, then the generator is faulty and should be replaced or repaired.
If the battery warning light comes on while the engine is running, stop the engine and check the condition and tension of the alternator drive belt and the wiring to the alternator.
Checking the voltage regulator
1. Connect a voltmeter to the battery terminals and start the engine.
2. Increase the engine speed until the voltmeter reading stabilizes, which should show from 12 to 13, but not more than 14 volts.
3. Turn on the maximum number of electrical consumers (headlights, rear window defroster, heater fan). In this case, the voltage generated by the generator with a voltage regulator should be in the range from 13 to 14 volts.
4. If the voltage does not meet the required values, the cause of the malfunction may be worn alternator brushes, weak brush springs, a faulty voltage regulator, a faulty diode, a broken stator winding, or defective rotor slip rings.