Replaced bad alternator, but battery light is still on! 1998 Ford F150

recharge the battery and once stated disconnect the neg cable, if it dies the alternator is bad,

It sounds like a short in your fuse box. They are known for this problem in these trucks.

Go through few Alternator related solved Solutions including replacement of alternator.Select and Click the link below:----How to replace alternator? http://schematicsdiagram.blogspot.com/2011/12/how-to-replace-alternator-on-gmc-sonoma.html
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How to test alternator on Dodge Stratus?

http://technoanswers.blogspot.in/2012/02/how-to-test-alternator-on-dodge-stratus.html

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How to test and replace Alternator on Audi A4 Car models?

http://repairhelpcenter.blogspot.com/2011/11/how-to-test-and-replace-alternator-on.html

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How to Remove Voltage Regulator on Car?

http://vwrepairhelp.blogspot.com/2011/11/how-to-remove-voltage-regulator-on-car.html

HOW TO REPLACE AN ALTERNATOR BELT

http://schematicsdiagram.blogspot.com/2011/08/how-to-replace-alternator-belt.html

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How to monitor Vehicles charging system? http://repairhelpcenter.blogspot.com/2011/11/how-to-monitor-vehicles-charging-system.html

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Car Alternator making noise? http://repairhelpcenter.blogspot.com/2011/11/car-alternator-making-noise.html

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After replacing Alternator, the battery indicator light Comes ON dash?

http://howtobyme.blogspot.com/2011/11/after-replacing-alternatorthe-battery.html

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How to inspect Vehicles Alternator?

http://repairhelpcenter.blogspot.com/2011/11/how-to-inspect-vehicles-alternator.html

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How to Test Vehicles Alternator?

http://repairhelpcenter.blogspot.com/2011/11/how-to-test-vehicles-alternator.html

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How to Service Vehicles Alternator?

http://repairhelpcenter.blogspot.com/2011/11/how-to-service-vehicles-alternator.html

How to Replace Alternator? http://repairhelpcenter.blogspot.com/2011/11/how-to-replace-alternator.html

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Alternator testing? http://schematicsdiagram.blogspot.com/2011/12/alternator-testing.html--------- Cars electrical system is pulsating? http://technoanswers.blogspot.in/2012/01/cars-electrical-system-is-pulsating.html------ 1998 Ford F150 pickup Battery Drains overnight due to Alternator? Alternator drains car battery? http://technoanswers.blogspot.in/2012/02/1998-ford-f150-pickup-battery-drains.html------- 2002 Ford Focus sits over night and battery goes dead? http://technoanswers.blogspot.in/2012/02/2002-ford-focus-sits-over-night-and.html--------- Charging system problem on Chrysler LHS car? http://technoanswers.blogspot.in/2012/02/charging-system-problem-on-chrysler-lhs.html---------- How to replace alternator 1997 Dodge Stratus? http://technoanswers.blogspot.in/2012/02/how-to-replace-alternator-1997-dodge.html------- How to replace Alternator on Mitsubishi Lancer http://www.howtorepairguide.com/2012/10/how-to-replace-alternator-on-mitsubishi.html
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These details will help.
For more help.Keep updated.
Thanks.
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check your surpentine belt first to make sure it is tight, if so it sounds like your alternator is going bad, its not pushing enough amps to charge the battery and run the truck that is why the light is on

alternator commutator/brushes on last legs

alternator.
the vehicle was running off the battery.
if the battery was bad,the truck would run fine off the alternator.
get an avr test done/

check the carbon brush alternitor if damage change

have you checked your voltage regulator?

i had this exact same problem ... under the hood onthe left side of the firewall where your starter solenoid and fuseable links are there is a little container type thing that holds a 20 amp fuse that fuse is probably blown the little container is on the firewall right below the fuseable links

ford falcon ea 1990
battery light is on
replaced battery and alternator but light id still on?
anyone has a solution?