Battery light
Hotshot
Joined: Jan 2002
Posts: 17,988
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From: La La Land
It's time to borrow a good volt meter if you don't already have your own, and read the voltage across the batteries when the engine's running at about 1800 rpm.
Voltage should read very close to 14.4 volts DC, which is the "set point" for them. You need to be able to accurately read down to tenths of volts for this. If you really are at 12-13, as you earlier noted, you've got a true alternator problem!
Pop
Voltage should read very close to 14.4 volts DC, which is the "set point" for them. You need to be able to accurately read down to tenths of volts for this. If you really are at 12-13, as you earlier noted, you've got a true alternator problem!
Pop
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Senior User
Joined: Aug 2004
Posts: 181
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From: Michigan
Thanks for the offer but I am near Holland, I was also thinking about stopping at an AutoZone or this one man auto electric shop. Do I have to remove it at Autozone or will they test in the truck?
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Senior User
Joined: Aug 2004
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From: Michigan
Tested at home 12.62v with truck off and 12.30v with truck at 1800 rpm. I will have to try to get to Autozone tomorrow.
From these measurements does it sound pretty definate a alternator?
From these measurements does it sound pretty definate a alternator?
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Hotshot
Joined: Jan 2002
Posts: 17,988
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From: La La Land
Yes. With no current drain at all, the battery is reading about par.
Add the small amount of current drain that a running vehicle typically draws, and it would drop a bit if there was no charging action.
If the alternator has field current flowing TO it, and nothing coming OUT of it, you may have a defective alternator. But first, you must now determine if the field has current available. It's a FUSED circuit, so this may be as simple as a blown fuse, too.
Check for voltage on pin "A" (OR/LB). If none, start checking for a blown field current fuse. It's a 10 amp, and I think it's #6 in the under-hood fuse and relay panel.
Pop
Add the small amount of current drain that a running vehicle typically draws, and it would drop a bit if there was no charging action.
If the alternator has field current flowing TO it, and nothing coming OUT of it, you may have a defective alternator. But first, you must now determine if the field has current available. It's a FUSED circuit, so this may be as simple as a blown fuse, too.
Check for voltage on pin "A" (OR/LB). If none, start checking for a blown field current fuse. It's a 10 amp, and I think it's #6 in the under-hood fuse and relay panel.
Pop
Last edited by SpringerPop; Dec 4, 2007 at 09:25 PM.
Mountain Pass
Joined: Jul 2004
Posts: 229
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From: San Diego, CA
When my battery light started flickering had the batteries tested. 1 was bad and the other was fine. Replaced the one. About a day later started back. I drove it like that for about a week. While I was on my way pulling my trailer with a car on it, it started not to charge and then would. Of course I was running at night. I made it about 100 miles before I had to stop and wait for the parts store to open up. Replace it and then a week later had to replace the other battery. New I should have changed alt before starting on the trip.
New User
Joined: Jan 2004
Posts: 20
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I just posted on another string I had the same issue, replaced top altenator in March, I had a bad batt in july replaced them both then just the other day Batt light flickers at low rpm's ended up being the lower alternator. One other item worth mentioning when the issue with my second alt started it just died going down the road, had to jump it and no time to trouble shoot so I took it by the stealer, they called and said that it was the pigtail from upper alt to voltage regulator, I had them fix it and when I picked it up I asked for the part. I did a continuity test and it failed, stripped the wires and there was a broken wire in there. This was not my ultimate issue but I do think that is why it died going down the road in the midst of my lower alt weakening.
New User
Joined: Jan 2004
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SpringerPop, when you say test voltage accross Batteries, what do you mean + on one and - on the other??? I was trying to test output on one alt vs the other and since they are in series I didnt feel I was getting accurate read. Wish I woud have found this post a month ago. I am glad they are easy to remove and test individually!
Postmaster
Joined: Nov 2003
Posts: 3,595
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From: Utah County, UT
[QUOTE=Izzy351]hhmmm... Sounds like a weak alternator to me. Mine came on and stayed on. Replaced with a new one (not reman) back in June and it has been fine so far. There is a place to get some really heavy duty alts, which I wish I knew about before I bought mine from AZ for almost $200. For not a lot more, I could've had a 160A heavy duty, or even a REALLY stout 200A...
http://www.alternatorparts.com/Ford_7.3_Power_Stroke_Diesel.htm[/QUOTE]
This is the place i bought my replacement from, have a few pic in gallery if you want to look. I am completely happy with it. I bought the 140AHD version. I also added some 4awg wire from the output to the driver side battery.
http://www.alternatorparts.com/Ford_7.3_Power_Stroke_Diesel.htm[/QUOTE]
This is the place i bought my replacement from, have a few pic in gallery if you want to look. I am completely happy with it. I bought the 140AHD version. I also added some 4awg wire from the output to the driver side battery.
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Senior User
Joined: Aug 2004
Posts: 181
Likes: 0
From: Michigan
Had alt. tested, bad. New one installed-light gone off dash and battery gauge showing more volts than before. I was pretty much running on batteries the last two days, my volts were down to 11.5. Problem gone.
Thanks for all your help!
Thanks for all your help!
Post Fiend
Joined: Feb 2007
Posts: 14,541
Likes: 2
From: Dallas-Ft. Worth
Originally Posted by Yukon
Had alt. tested, bad. New one installed-light gone off dash and battery gauge showing more volts than before. I was pretty much running on batteries the last two days, my volts were down to 11.5. Problem gone.
Thanks for all your help!
Thanks for all your help!