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with engine running, remove negative(black) battery cable. If engine dies, it's your alternator.
The person who answered this question really shouldn't be answering questions on this subject.
While it is true that this USED TO BE (in the 40's to mid 70's) a quick and safe test to reveal if the alternator (or generator) was charging; do the same thing to some of the newer vehicles and you will be replacing an alternator or an ECM because you "fried" it with your old fashioned test.
The correct answer would be to load test the battery (auto zone, pep boys etc, will do it for free, just drive up and ask) and load test the alternator at the same time.
What else can I help you with?
Why isn't your Mazda truck alternator not charging your battery?
bad alternator, bad voltage regulator, bad battery, bad connections.
How do you wire alternator to a battery to test alternator?
run it and then disconnect the negative wire from the battery if alternator dies its bad.
Why does the battery light stay on after replacing the alternator 2009 Chevy Malibu?
You might have a bad battery, a poor connection between the battery and alternator, or a bad ground from the battery.
MY car battery light is still on after the alternator and the battery has been changed. The battery cables are clean and well attached. Now what?
Battery light usually means alternator not charging. Most common solutions would be be a bad alternator, bad connection, or loose alternator belt. A replacement alternator can be bad. If it is ok than most likely a poor connection to the alternator.
What can make a car battery die when running?
It sounds like the alternator is bad. If the alternator is bad the battery will not hold charge when running
Will a bad alternator keep a 1999 S10 pickup truck from starting?
The answer is no . The battery starts you vehicle , the alternator charges the battery so if your alternator is bad your battery is not receiving a charge which will cause a "no start" condition.
Why won't the alternator charge?
Bad alternator? Bad voltage regulator? Bad Battery (won't take a charge)? Bad fusable link? Loose or corroded battery cables?
My alternator is not getting power from the battery The wiring from the battery to the solenoid and from the solenoid to the alternator is good is this a bad solenoid the car will start and run?
Check for a bad fusable link at alternator
Why is the Battery light stuck on in my 1996 ford contour battery seems to be fine along with the alternator...?
Battery light usually means alternator not charging. Most common solutions would be be a bad alternator, bad connection, or loose alternator belt. If the battery and alt test ok than check the connections to the alternator and battery.
Why does the battery light come on a 1996 Ford Exployer after changing the battery and having the alternator checked?
Battery light usually means alternator not charging. Most common solutions would be be a bad alternator, bad connection, or loose alternator belt. If the battery and alt test ok than check the connections to the alternator and battery.
What will bad alternator do to a cars battery and lights?
A bad alternator will have the effect of draining the battery, resulting in dim lights, trouble starting the car and the like. It would be best to replace the alternator as soon as possible and possibly obtain a new battery. This may vary depending on how much the bad alternator has drained it. You can get your alternator and battery checked any time at Auto Zone.
How can I test my alternator to see if it is discharging my battery?
You can have the alternator tested free of charge at just about any major auto parts store. By the way, a bad alternator will not "discharge" a battery - the alternator's function is to provide the charge to the battery. If the alternator is faulty, then it is not providing the charge necessary to keep other components from discharging the battery. I had the alternator tested and it was charging. If the alternator has a bad diode, it will discharge the battery. I replaced the alternator and everything is fine.
