Alternators
Car Batteries

Why does the battery light stay on even after the alternator has replaced?

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2005-10-11 14:46:33
2005-10-11 14:46:33

Find a volt meter, check the battery voltage with the engine stopped, it should be a around 12 V. Now start the engine and the voltage should be around 13.5 V. If the alternator isn't putting out about 13.5 (+/- .5 V) the replacment alternator could be bad or you might have a bad connection somewhere.

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The battery light isn't an indicator that the battery is always bad. What the light should really be is a picture of an alternator, but most people wouldn't recognize that. Have the alternator checked off the vehicle to make sure it is good, then have it checked on the vehicle, (many places like Auto Zone do this for free). If it's not charging on the vehicle, you could have an alternator fuse bad or your car might even have an inline fuse between the alternator and battery. Many Ford products have a large fusible link between the alternator and battery, and if it's bad, there is no power going to the battery from the alternator. Good Luck!!!!

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You're right it could be a dead battery, the starter, the soleniod, or even the alternator. My guess try jumping the car or charge the battery.

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Some new alternators will not charge unless the battery has a full charge already.

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Sometimes even though the voltage at charging is good the battery or alternator could be low on charge or charging low for your vehicles specs.

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bad alternatornot always.if its a bad battery and can't hold a charge the same thing will happen.I had a 99 s-10 that would occasionally die at the pump or even while driving, I had a new defective battery, replaced under warranty, no more problem.I would have the alternator checked out before replacing it if that is the problem. I had my replaced and it wasn't cheap...$630 to be exact. The new alternators run around $200 and most mechanics will change the serpentine belt when they replace the alternator so this MAY be an added expense.If the alt is working properly, you can remove one of the battery cables while the engine is running and it will continue to idle. If it dies then the alt needs to be replaced.

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Then the alternator needs to be looked at asap But I even took the cable off alternator and car stayed on which meet alternator in good right? Edit: If you took the cable off the alternator, then you disconnected the alternator so you didn't test the alternator at all. As a quick test only, removing the positive battery cable at the battery and the engine stays running means the alternator is charging. Do not run the engine more than a few seconds like this, and even then a voltage spike can wipe out your car's electronics. Much better to get a charging system tester to check things or at least borrow a voltmeter.

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Something is causing a drain on the battery even with the vehicle off and nothing turned on. A good mechanic can do a drain test on the battery to see what may be draining the charge. A dead cell in the battery itself will also cause the battery to go dead. Disconnect the negative battery cable overnight and if the battery is dead the next morning it has a dead cell and must be replaced. If not look for a light that is on or a relay that is stuck.

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Since you replaced the battery and alternator, you must have had a problem before. Did you run a voltmeter on the battery while the engine is running? Should have around 14 volts. If you are getting around 14 volts, you can assume that the lite might be faulty. If you are getting say, 12 to 13 volts, then the alternator might be faulty, yes even sometimes rebuilt ones. Check all the wires to make sure there is good contact, also if you still have the problem, then you might have a broken wire ( somewhere ). Good luck


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