Circuit failure caused by reverse polarity of car battery
Fault phenomenon: After the ignition switch of Isuzu is turned off, the instrument displays normal, but the charging indicator light does not ignite. When the ignition switch is placed in the second gear (starting gear), the starter does not respond.
Check the charging LED, the charging LED shows good. Since the car charging indicator is controlled by a combination relay, the combination relay was removed for inspection and no problems were found.
Refer to the wiring diagram of the automobile integrated relay circuit, it can be seen that when the engine is not working, when the ignition switch I or II is turned off, the charging LED will be ignited by electricity. 'The current is charged by the battery's positive ignition switch, charging indicator, combination relay and the normally closed contacts of the relay. After turning off the ignition switch, the car's charging lamp does not light up. It is believed that this is due to the opening of the normally closed contact of the charge indicator relay, so it is suspected that there is voltage at the power supply terminal of the charge indicator relay at this time. Car charging shows that the relay power supply is connected to more IG connectors, thus eliminating the disassembly inspection and finding that the diode on the positive rectifier board has been disconnected and short-circuited. After replacing the diode.
When the diode on the positive rectifier board is disconnected and short-circuited, the B-pillar of the alternator and the short-circuit diode/short-circuit diode are connected to the battery current, and IG is connected to the pole/charge indicating relay The coil will tie up the iron. 'In this way, the charging indicator relay can be operated, and its normal closed contact is also closed, thereby cutting off the connection circuit between the charging indicator and the starting relay, and the above-mentioned fault occurs when the ignition switch is turned off.
It should be pointed out that the short-circuit fault of the diode is caused by the car driver connected to the battery polarity, and the battery current flows through the rectifier diode without any load.