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Alternator charging problem?

Tiny
COYOTEMAYHEM375
  • MEMBER
  • 1993 FORD F-150
  • 5.0L
  • V8
  • 4WD
  • AUTOMATIC
  • 151,235 MILES
While running I have a good charge, if I turn on my AC or heater the voltage drops to around 9 volts. If I push up/down on windows while they are up/down the voltages drops real low and bounces around. Sometimes when I come to a light it will drop to about 10 volts. Both battery and alternator test good.
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Friday, June 29th, 2018 AT 9:26 PM

21 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,913 POSTS
Hi and thanks for using 2CarPros.com.

It sounds like the alternator is bad and cannot keep up with the demand. Here is a simple test to check if it is working:

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Try that test and let me know what you find. Additionally, if you are not comfortable doing it yourself, most parts stores can check it on the vehicle and will do it for free.

Let me know what you find or if you have other questions.
Take care,
Joe
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Sunday, July 1st, 2018 AT 6:37 PM
Tiny
COYOTEMAYHEM375
  • MEMBER
  • 4 POSTS
The battery and alternator was tested at a parts store. Both were fine, even put a brand new alternator on for good measure and it was still the exact same.
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Sunday, July 1st, 2018 AT 7:08 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,913 POSTS
Is the serpentine belt self adjuster keeping everything tight?
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Sunday, July 1st, 2018 AT 8:08 PM
Tiny
COYOTEMAYHEM375
  • MEMBER
  • 4 POSTS
Yes, idle voltage is fine at idle and above idle.
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Sunday, July 1st, 2018 AT 8:20 PM
Tiny
COYOTEMAYHEM375
  • MEMBER
  • 4 POSTS
If it is below 45° it takes about ten minutes to start charging in the morning as well.
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Monday, July 2nd, 2018 AT 11:13 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,913 POSTS
Hi again. If the alternator and battery are good, I would start checking grounds. A weak ground could be an issue. Also, confirm that the fusible link is in good condition and making good connection. I have attached a wiring schematic for your vehicle. Take a look at it and let me know if this helps.

Note: I had to get two pictures for the entire schematic. Sorry about that.

Let me know.
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Monday, July 2nd, 2018 AT 7:56 PM
Tiny
GIZMO69
  • MEMBER
  • 1 POST
  • 1993 FORD F-150
  • 6 CYL
  • 4WD
  • MANUAL
  • 200,000 MILES
My truck is not charging and I have changed alternator and nothing. I have three wires going into one fusible link. Could this be the starter?
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Friday, January 22nd, 2021 AT 11:40 AM (Merged)
Tiny
BILLYMAC
  • MECHANIC
  • 2,204 POSTS
Hi if it is not chargeing it has to be in the charge system. Check plug at alt check all fuse links check voltage regulator. Check all fuses good luck feel free to write again billymac
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Friday, January 22nd, 2021 AT 11:40 AM (Merged)
Tiny
MICHAEL DUCKWORTH
  • MEMBER
  • 1 POST
  • 1993 FORD F-150
  • 5.0L
  • V8
  • 4WD
  • MANUAL
  • 149,000 MILES
I did an automatic to manual transmission swap. New starter hooked everything up like it came out. Cranked the truck while it was idling the interior light went out. Checked alternator it was bad. Put new one on still no charge. I have looked at everything still nothing.
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Friday, January 22nd, 2021 AT 11:41 AM (Merged)
Tiny
CARADIODOC
  • MECHANIC
  • 33,945 POSTS
Most commonly you will find the brushes are worn. Those come as part of a new voltage regulator. The regulator can be replaced separately by removing the four bolts in the four corners of the regulator. The new one will come with a toothpick in the hole just to the right of my blue arrow. Leave that in place while you bolt the new regulator to the generator. Once finished, the last step is to slide out that toothpick. You'll hear two faint clicks as the new brushes snap into place.
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Friday, January 22nd, 2021 AT 11:41 AM (Merged)
Tiny
PHILLIP MORRIS
  • MEMBER
  • 6 POSTS
  • 1992 FORD F-150
  • 10,000 MILES
Alternator works OK and Battery is OK, but the system will not charge. Is there a fuss link in the charging system. I have a green and red strip wire from the Alternator that is not hook up could that be the problem?

I have had the Alternator check at 2 places and they read the same. The Battery in new. I have check all the wiring from the Alternator and found a green with a red strip on it but can not find where it hooks up. Also does the charging system have a fuss link in it.
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Friday, January 22nd, 2021 AT 11:42 AM (Merged)
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
Yes the wiring needs to be tested the green and red wire goes over to the voltage regulator. Here is a couple guides that will help you get the problem fixed. The voltage regulators are separate on this truck on some models.

https://www.2carpros.com/articles/how-to-check-wiring

and

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

Here is a wiring diagram (below)

Please let us know what happens.

Cheers
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Friday, January 22nd, 2021 AT 11:42 AM (Merged)
Tiny
PHILLIP MORRIS
  • MEMBER
  • 6 POSTS
OK his some more on the charging system problem. I took my meter and check all the wiring, the fuses have been removed before I bought the truck. I have load tested the charging system and still now power coming through. I took the leads of the Alternator that go to the starter rely, they should be hot all the time. I removed them and check for power no power while it was running from the alternator. I pulled the alternator and check all the wiring they have a clear path. But I check the rest of the Alternator nothing
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Friday, January 22nd, 2021 AT 11:42 AM (Merged)
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
I posted the wire diagram for the alternator there are 3 power inputs coming into the alternator from a fuseable link. See if you have those three power inputs into the alternator.
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Friday, January 22nd, 2021 AT 11:42 AM (Merged)
Tiny
PHILLIP MORRIS
  • MEMBER
  • 6 POSTS
I have the same diagram as the one you have sent me. The fuss able links where all removed some time ago and the wires where routed back to the same points less the fusses. The system has worked ever scent I have owned the truck, until lately it will not charge the battery up. I cut the power lines from the Alternator and fired the truck up and check the out put no out put from any point of the Alternator. So I am figuring the Alternator is got to be the trouble. I am going to have it bench check one more time or just get a new Alternator. This getting nuts. Its a simple system almost like a two wire Alternator. Oh well.
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Friday, January 22nd, 2021 AT 11:42 AM (Merged)
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
With everything hooked up was there power going to those three wires at the alternator?If not you have to start by getting power there and adding a fuseable link also.
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Friday, January 22nd, 2021 AT 11:42 AM (Merged)
Tiny
PHILLIP MORRIS
  • MEMBER
  • 6 POSTS
The two lines you see on the schismatic that come off the alternator they go to the starter rely from there one goes to the battery and one to the starter. So between the alternator and rely they our hot all the time so long ass they our still connected to the battery. But when you start the engine and load the electrical system the alternator does not go up in charge. If you remove those cables so they our not pulling from the battery there is no power on the lines, being this is the lines that charge the battery there should be power there while the alternator is running but there is no power. You pull the alternator off the truck to bench test it you get 13.8 volts on the bench test. All test our done with a full charged battery. So I am assuming there has to be a short in the alternator I will have it check one more time.I think it will have to be the alternator every thing else checks out OK. But why on a bench it shows OK? But when you connect it to the truck nothing?
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Friday, January 22nd, 2021 AT 11:42 AM (Merged)
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
Without power going into the alternator it wont charge also with the key in the run position and engine off do those three wires off the fuseable link in the wire diagram I posted have battery voltage going into the alternator?Sounds like you have no power to one or all those wires.
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Friday, January 22nd, 2021 AT 11:42 AM (Merged)
Tiny
PHILLIP MORRIS
  • MEMBER
  • 6 POSTS
Yes the three wires have power. But still no generation from the alternator. Its just about like a two wire alternator it so simple thats why I figuring some tester have to be wrong.
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Friday, January 22nd, 2021 AT 11:42 AM (Merged)
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
Are the two white wires with the black strip connected together?
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Friday, January 22nd, 2021 AT 11:42 AM (Merged)

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