Charging System Diagnostics


Old 05-25-02, 10:09 PM
thiggy's Avatar
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Question Charging System Diagnostics

I have been told that one way to check if you have a defective alternator or generator is to crank the vehicle and disconnect the battery. If the engine continues to run, the alt/gen is OK. If it dies, the alt/gen or some component of the charging system is defective. Is this a reasonable test? Is there a more definitive way to check the charging system with a standard shop multi-tester? The car I am actually trying to resuscitate is a 1967 Datsun 411 with the 1600 cc engine. It has been parked for 4 - 5 years and required a major clean-up of gunk in the fuel line and gas tank before I could get fuel to the carbs. I finally got it running, but when I disconnect the battery the engine dies.
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Old 05-26-02, 08:43 AM
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Some vehicles will run with the battery disconnected and others will not, so not really a valid test. With the engine running, check voltage at the battery. Depending on the vehicle and alternator you should probably be seeing somewhere around 13.5-14.5 volts. At that age it may have an external regulator which could also be the culprit of any chagring problems. This is not a definitive test because there is amperage invloved, too, but it's a start. I'm assuming you dropped a new battery in it during the revival?
Old 05-26-02, 09:17 AM
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Definitely not a valid fact a great way to wipe out the diodes in the alternator.

TowGuy gave you a much better way to check it...and more accurate too.

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