# battery light



## s. donato (Dec 9, 2010)

hey guys since it has gotten colder when ever i start my truck from a cold start the bettery light comes on. My SG2 says voltage is in the 11-12 range until the truck gets up to full running temp which is after about 30 mins of run time.

i just replaced both batteries b/c it thought one was going. but now i am thinking the alternator that i put in right before i replaced the batteries may be the problem. :realmad: i already told my mechanic to get a replacement b/c i feel that its not working right.

anyone else experience this before? a couple friends of mine said it more then likely is the warm up process(they have ford diesels too) but they agree its taking a bit long to get back to 14 volts on the meter.


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## dieselss (Jan 3, 2008)

Anytime the batt light comes on,,,its the alt. the diodes in the alt are bad/going bad an that causes the light to come on, just replace the alt and you'll be fine


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## abbottfarm (Dec 27, 2010)

Yeah, probably your ALT. Make sure when you buy a new replacement you have it bench tested before you pay for it. You would be surprised how many are junk right out of the box.


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## s. donato (Dec 9, 2010)

yeah the one i got was rebuilt from a very reputable guy. it took one call and he said bring it in for a replacement free of charge(no charge for install). i thinking of getting a NEW one and then keeping his rebuilt that they put in tomorrow as a back up. as i drove home tonite from work it according to my SG2 it was only at 13.1 after 30 mins of city driving.


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## 2COR517 (Oct 23, 2008)

s. donato;1379991 said:


> hey guys since it has gotten colder when ever i start my truck from a cold start the bettery light comes on. My SG2 says voltage is in the 11-12 range until the truck gets up to full running temp which is after about 30 mins of run time.
> 
> i just replaced both batteries b/c it thought one was going. but now i am thinking the alternator that i put in right before i replaced the batteries may be the problem. :realmad: i already told my mechanic to get a replacement b/c i feel that its not working right.
> 
> anyone else experience this before? a couple friends of mine said it more then likely is the warm up process(they have ford diesels too) but they agree its taking a bit long to get back to 14 volts on the meter.


So it does eventually get to 14+ volts?



dieselss;1380342 said:


> Anytime the batt light comes on,,,its the alt. the diodes in the alt are bad/going bad an that causes the light to come on, just replace the alt and you'll be fine


Does that mean worn brushes or a shorted stator field won't cause the light to come on? What about an open armature?


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## MickiRig1 (Dec 5, 2003)

Should be 14.5 volts with the truck running. If it's not, the alternator is toast or soon to be.


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## dieselss (Jan 3, 2008)

The Batt light on means that the diodes are going bad/are bad internally. You could replace them, but why? Take the alt apart find the diode pack and then try and out it back together? Nah new one


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## GL&M (Sep 26, 2005)

dieselss;1380342 said:


> Anytime the batt light comes on,,,its the alt. the diodes in the alt are bad/going bad an that causes the light to come on, just replace the alt and you'll be fine


I just replaced one that wasn't charging at idle. When running and the RPMs were up it charged. If you let it sit at idle for a while and shut it off, it wouldn't start. New alternator and the problem went away.


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## 2COR517 (Oct 23, 2008)

dieselss;1380342 said:


> Anytime the batt light comes on,,,its the alt. the diodes in the alt are bad/going bad an that causes the light to come on, just replace the alt and you'll be fine





2COR517;1380976 said:


> Does that mean worn brushes or a shorted stator field won't cause the light to come on? What about an open armature?





dieselss;1382536 said:


> The Batt light on means that the diodes are going bad/are bad internally. You could replace them, but why? Take the alt apart find the diode pack and then try and out it back together? Nah new one


I guess I'm confused. The only thing that makes the light come on is a diode failure? Other failures wont make the light come on? And what's the difference between an internal and external diode failure?

Maybe you know this also. Someone told me once that automotive alternators produce three phase power. Is that true?


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## MickiRig1 (Dec 5, 2003)

The thing with replacing just the diodes is the rest of the alternator is also tired. You have the bearings, voltage regulator, windings and brushes that are tried. A plow truck alternator gets spanked every time you work the truck for a while. It has a huge heat load each time! Just replace it or upgrade the alternator output and the wire to the battery / batteries. Make sure the belt is good and the belt tensioner is good.


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## 2COR517 (Oct 23, 2008)

Where did dieselss go? I was hoping he would answer those questions....


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## s. donato (Dec 9, 2010)

seems like it was the alt. its weird the guy bench tested it after it was removed from the truck and it was charging fine. i think it was pretty much doing that from time to time b/c the day it got removed my voltage was in the 13's but the whole week it was 12's and low 13s. but new rebuilt is now in and i haven't seen it go below 13.6 so far. i need to drive the truck a bit more before i can say for certain.


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## TerraScraper (Dec 10, 2008)

Keep us posted, my light is flickering as well in my 6.0. how many miles on your truck?


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## s. donato (Dec 9, 2010)

70k but just bought the truck so not sure if it was original alt.


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## dieselss (Jan 3, 2008)

I'm back donato lol Scheech can't a guy take a break lol. J.k. the alt does produce 3 phase electricty, thats the diodes job to convert it to single phase. And yes to the light q? Thats the only reason the light will come on. Or when you just turn the key on. No a days alts only have "internal" parts so theres nothing external to "play" with. If the its now putting out 14+ with a load on it it bad. Dont always go by what the factory gauge is telling you when you cking it. Get a meter on it.


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## s. donato (Dec 9, 2010)

I have a scan gauge and when i checked it against the meter directly conectted to the alt we had a .1-.3 difference so that's why i know 13.8 isn't that bad b/c when we checked it against the meter - the meter had 14.1.

anxious to hook up my plow and move it around a bit and see what happens ;-)


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## dieselss (Jan 3, 2008)

It'd prob gunna be ok, now. Not gunna be ok when you need it the most. I would disregard the bench test, and just replace it.


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## s. donato (Dec 9, 2010)

no i agree dieselss. i had them give me a new one which is why i know this one is alot better already. had the heated seats going while driving around this morning with the SG2 saying 14.1 the whole time - it did bounce around a bit from 13.8-14.2 but that's a much smaller window then the 11.2-13.8 from the one i had them take back.


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## dieselss (Jan 3, 2008)

Oh yea. 11v it was toast. Did you get an upgrated one? Upgrade your output wire? Add a gnd wire to the alt?


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## dieselss (Jan 3, 2008)

Did forget to ask. What truck and motor?


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## s. donato (Dec 9, 2010)

i have a 2004 6.0 CCSB lariat.

i had to replace the factory positive terminal on b/c they were corroded when i did the original alt about a month ago.

i now have a slightly upgraded rebuilt. he told me i had a factory 140 amp alt before i have no clue what this one is. other then he said he upgraded this one for a diesel. which i said quite pissed off "i have a diesel why wouldn't you give me this one before!!!" ;-)

where would you attach a ground off the alt? i sure can do it if you tell me how ;-)

about to wire up the stereo system this week. i have some extra 4 gauge i can use and make a ground wire for it. ;-)


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## dieselss (Jan 3, 2008)

For the alt out put and gnd I would run 2 gauge or bigger. The gnd, if you don't have a place on the back of the alt, just put it on one of the mounting bolts


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## s. donato (Dec 9, 2010)

mounting bolt to the neg terminal on the battery or body?


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## dieselss (Jan 3, 2008)

Batt only. As little resistance as possible. Going to the body is like going through a middle man, go right to the source


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## s. donato (Dec 9, 2010)

makes sense. thanks


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## mustangman02232 (Mar 21, 2011)

s. donato;1380854 said:


> yeah the one i got was rebuilt from a very reputable guy. it took one call and he said bring it in for a replacement free of charge(no charge for install). i thinking of getting a NEW one and then keeping his rebuilt that they put in tomorrow as a back up. as i drove home tonite from work it according to my SG2 it was only at 13.1 after 30 mins of city driving.


is he going to give you a new FICM to from his alternator dieing? dont deal with used crap, buy a new ford one out of the ambulance package. (mine was $160)


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## s. donato (Dec 9, 2010)

i just hooked up my plow to move it around and had the voltage dropped to 12.8 it bounced back right up to 14.1 but it was dipping down in the 13's pretty good. 

might i add that i have two brand new die hard platinum batteries! i never had this issue with my dakota running a 140 alt and one platinum battery.

i am really pissed at this moment!!! is it the diesel that pulls more amps then a gaser?


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## mags11 (Oct 7, 2012)

Don't know if it's true, but I heard if you run the plows wiring harness over "things " you're not soposed to, will make your battery light come on. Sorry, maybe someone else can tell ouu what those "things" you are soposed to avoid are.


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## dieselss (Jan 3, 2008)

No. Only a bad diode inside the alt will turn on the BATT light on


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## 2COR517 (Oct 23, 2008)

dieselss;1574044 said:


> No. Only a bad diode inside the alt will turn on the BATT light on


What about bad brushes?


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## dieselss (Jan 3, 2008)

I'm Gunna say no. Just the diodes. If electricity flows in the opposite direction it will back feed and turn on the light


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## 2COR517 (Oct 23, 2008)

So failing to charge won't turn the light on, but a three phase AC sine wave output will.

Learn something everyday.


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## dieselss (Jan 3, 2008)

Yep.....only other time it will turn on the light is if key is on,,like in acc. Or when engine is running but the alt isn't turning


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## 2COR517 (Oct 23, 2008)

So the electricity must be flowing backwards into the alternator with the key on engine off?


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