Symptom: After an Isuzu car closes the ignition switch, the meter display is normal, but the charging indicator does not light, and the starter does not respond when the ignition switch is placed in the II position (starting gear).
Troubleshooting: Check the charging indicator and the charging indicator shows normal. Because the car's charging indicator is controlled by the combination relay, the combined relay is removed for inspection and no problems are found.
Referring to the wiring diagram of the vehicle combination relay circuit, when the I or II gear of the ignition switch is closed when the engine is not running, the charging indicator light will be brightened by the power supply, and the current is from the positive battery → ignition switch → charging indication Lamp → Combined relay The normally closed contact of the charging indicating relay → ground. The charging indicator of the car is not lit after the ignition switch is turned off. It is considered that it should be caused by the normally closed contact of the charging indicating relay being disconnected. Therefore, it is suspected that there is voltage at the power terminal of the charging indicating relay. The vehicle charging indicating relay power terminal is connected to the alternator IG connecting post, so the alternator decomposition check is removed, and it is found that one diode of the alternator is rectifying and short-circuited. After replacing the diode, troubleshoot.
After a diode of the alternator is rectifying and short-circuited, the battery current will be charged by the alternator armature B+ post → the short-circuit diode → alternator, IG post → charging indicator relay coil → grounding, so that charging The relay is energized to open its normally closed contact, thereby cutting off the grounding circuit of the charging indicator and cutting off the grounding circuit of the starting relay, so the aforementioned failure occurs when the ignition switch is closed.
It should be pointed out that the diode is short-circuited because the driver of the vehicle has mistakenly reversed the polarity of the battery, causing the battery current to flow through the alternator rectifier diode without any load.
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