# Battery light comes on



## chevyzrule810 (Oct 5, 2010)

My friend has a 2007 Ford F-350 diesel.Truck has been alittle trouble to start lately.After charging the batteries we determined it was the alternator.Installed a new alternator.On the way home the battery light came on.Once he got home he shut it off and hasn't tried to start it since.The harness plug that plugs from the truck into the alternator is fine.Could it be a bad alternator?


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## BossPlow2010 (Sep 29, 2010)

Check fuse # 6 and 7


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## Randall Ave (Oct 29, 2014)

How did you determine the alternator failed? Did you test the new one, and how old are the batteries?


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## iceyman (Mar 1, 2007)

Battery might be toast


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## leolkfrm (Mar 11, 2010)

not sure on ford, my gmc has 1 module controlling the light and another the guage (ecm,bcm)
had no volts and light was on, confirmed only 12v when running, 
changed alt, volt gauge was happy light was not, had 14.2 at the batteries when running, 
changed the alt again all was good.....
bad rebuilt alt, 
most likely the original problem was not found with 1st rebuild


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## Mark Oomkes (Dec 10, 2000)

Where did the alternator come from?

Did you test the batteries?


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## SnoFarmer (Oct 15, 2004)

Mark Oomkes said:


> Where did the alternator come from?
> 
> Did you test the batteries?


What answer are you looking for?
Napa?


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## chevyzrule810 (Oct 5, 2010)

The battery's are alittle over 2 years old.We tested the battery's and one tested at 12.6 and the other at 12.4.We started the truck up and the voltage dropped down to 10.6 then 9.8 with the headlights on and shut off when we disconnected the negative terminal on battery.So we brought it to Napa and they tested it and said it was bad so we got a new one and gave them the old one for the core.Installed the new one.He got it home opened the hood and the connector that goes to the alternator was in the plug but not plugged in.It has been fine since.He put the connections on while I put the belt on so he must have forgot to plug it in all the way.


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## leolkfrm (Mar 11, 2010)

^^^ that will do it every time:hammerhead::laugh:


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## mjs91085 (Jan 11, 2016)

Friend of mine installed a new alternator in his truck.When you start it up the battery light won't come on but once the truck warms up the battery light comes on.What would cause this? And is there a fix for it?


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## Randall Ave (Oct 29, 2014)

mjs91085 said:


> Friend of mine installed a new alternator in his truck.When you start it up the battery light won't come on but once the truck warms up the battery light comes on.What would cause this? And is there a fix for it?


Lacking lots of information there. Year, make, model, what motor, ya know, stuff like that.


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## leolkfrm (Mar 11, 2010)

mjs91085 said:


> Friend of mine installed a new alternator in his truck.When you start it up the battery light won't come on but once the truck warms up the battery light comes on.What would cause this? And is there a fix for it?


yes, take it back for another one, its bad


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## dieselss (Jan 3, 2008)

Only main thing that causes the alt light is the alternator diodes (internal) or lonnnnngggggg shot......wiring got pinched.


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