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My alternator quit charging

Tiny
BKM48198
  • MEMBER
  • 1994 FORD RANGER
  • 190,000 MILES
Truck listed above is a 4x4 with a 4.0L I have tried 4 other alternators and none have worked, all 4 came from junkyards. My truck quit charging the battery so I assumed the alternator was bad, since then I have installed 4 other used alternators and none are charging the battery. I have checked the wiring and get 12v on the large wire from the solenoid that bolts on the back, I also show 12v on 2 of the 3 wires that plug into the alternator with key on engine off. Wiring seems to be good, battery light is on when I turn the key on and stays on when running. 12v at the back of the alt. So I assume the fusible link is good. Any ideas why I keep having problems, I doubt if all 4 alternators were bad but they could have been. Any ideas? Money is very tight so I don't want to spend $100.00 and still have the same problem.
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Saturday, November 5th, 2011 AT 3:39 AM

34 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Before we get too far, we need to take this alternator and have it load tested. If it passes then we can move onto the next thing but this has an internal regulator so this would be the likely issue even though you replaced so many of them.

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

The next thing is we need to make sure you are checking the S terminal and I terminal.

I attached the testing below that will walk you through this.

Please let us know what you find with this and we can go from there. Thanks
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Thursday, December 10th, 2020 AT 8:39 AM
Tiny
FIXITMR
  • MECHANIC
  • 9,990 POSTS
Here ya go.
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Thursday, December 10th, 2020 AT 8:39 AM
Tiny
BKM48198
  • MEMBER
  • 10 POSTS
I have the 2nd diagram and have been working off of it, the battery light comes on so I have 12v thru that wire (LG/R), I also have 12v at the (Y/W) wire and 0v on the (W/BK) with key on engine off.I have only seen 1 fusible link by the solenoid and it checks out good with 12v at the back of the alternator. Fuses all check out good but no charge when running.
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Thursday, December 10th, 2020 AT 8:39 AM
Tiny
FIXITMR
  • MECHANIC
  • 9,990 POSTS
I always take the alternator to the auto store for testing when I get them from bone yard. That way I know any problems originate with vehicle.
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Thursday, December 10th, 2020 AT 8:39 AM
Tiny
BKM48198
  • MEMBER
  • 10 POSTS
I made the alternator work by running 12v to the G/R & Y/W wires so I know the alternator is good, took the 12v off the Y/W wire and get no charge so I ran 12v from battery to Y/W wire only (OE wiring on G/R) and get charge but the battery light stays on in the truck, getting about 14.6v to the battery now. Battery charger is on now charging it because it was down under 12v. Thru the OE wiring when running I had 1.9v on Y/W wire and 6v on G/R wire, tried different fuses in power box under hood( 40a & 15A) with no changes. Something is still wrong but at least I know the alternator is good.
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Thursday, December 10th, 2020 AT 8:39 AM
Tiny
BKM48198
  • MEMBER
  • 10 POSTS
Fuses are all good, tried other fuses from my wife's car. Solenoid wires have not been touched in years, everything else works properly other than the charge circuit, I will try unhooking the solenoid and cleaning the terminal to see if that makes any difference but it shouldn't, the Y/W wire comes from the power box under the hood not straight from the solenoid. The things that I wonder about is if there is another fusible link somewhere that I have not found, and why does the voltage on the Y/W wire drop from 12v down to about 1.9v after starting the motor? I have a Chilton manual and have the wiring diagram for a 94 ranger and it shows the Y/W wire being straight thru from the 15a fuse to the alternator. I went and bought wire and connectors today so I can replace the wire tomorrow and see if that makes any difference.
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Thursday, December 10th, 2020 AT 8:39 AM
Tiny
CJ MEDEVAC
  • MECHANIC
  • 11,005 POSTS
Okay, the pic I posted earlier was not the one I meant to

I went back into Mitchel i, this is the one I meant to post

I really hope when you clean the solenoid connections, all will be good. Any other connections that are there (snap together smaller wires, in the system) might pull them apart a few times, do the dielectric grease thing to them also.

Here's the right pic.

Keep us posted,

The medic
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Thursday, December 10th, 2020 AT 8:39 AM
Tiny
FIXITMR
  • MECHANIC
  • 9,990 POSTS
Yah, that 1 only shows 1 fuselink. Which is what he has.
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Thursday, December 10th, 2020 AT 8:40 AM
Tiny
CJ MEDEVAC
  • MECHANIC
  • 11,005 POSTS
How are you determining your voltage

Gauge in truck---or a portable voltmeter?

Just for making sure you do not know another feller with a post here, the truck must be running in order to charge the battery!

If you had one of these, you'd be ridin' right now. Lol!

The medic
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Thursday, December 10th, 2020 AT 8:40 AM
Tiny
BKM48198
  • MEMBER
  • 10 POSTS
I have a digital volt meter for checking voltage. I do know the motor must be running to charge the battery, I have worked on my own vehicles for over 3o years, my grandfather owned a gas station, and my father taught me a lot about working on vehicles, mechanical things I have no problems with but electrical gremlins get me. What I have found is I get 12v at the Y/W wire with the connector unplugged key on/engine off, but after starting and connecting the plug to the alternator it only has 1.9v which is not enough to start the alternator charging. I had been assuming that I had 12v with it plugged in also and you know what happens when you ass/u/me!

If I had one of those I'd have to have my Carharts on since it's in the upper 30's outside tonight, but I did see a guy driving a Shelby Cobra (Kit Car) today when it was about 50 outside. He was bundled up pretty good in it, had to have been cold driving it today.
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Thursday, December 10th, 2020 AT 8:40 AM
Tiny
CJ MEDEVAC
  • MECHANIC
  • 11,005 POSTS
Just checkin'--you'd have to read some of these posts to understand why I ask "dumb" questions

Have you cleaned your solenoid connections? Just guessing you have ring ends stacked on the battery cable side, I hope that if you clean 'em up a bit, you will get your connection, and all will be fine

Can you read my diagram well. If not, I can send you a private message, you give me your email in there (not broadcasting it in open forum) I must initiate, you have to have 10 posts before you can initiate a message

How have you checked the fusible link? Continuity?

I'm lookin' at your diagrams on a 32" monitor

The only thing you might do that maybe you have not done yet, is to disconnect the battery let it sit 10 minutes---connect back in with a fully charged battery (not jump it off, still connected) on some rigs the computer must reset by a total disconnection. Like I said, imma jeep guy, i'm not used to something overriding normal older vehicle systems. Ie, a skip in my jeep, can usually be attributed to ezily found/ replaceable/ inexpensive componentsnot a bunch of codes or sensors that sometimes "cloak" the real problem!

'Nother thing you might try is to disconnect the battery, run a continuity test thru all of your wiring that is involved.I have found it to help me discover problems that test lights or voltage checks may miss

If you don't know how to do continuity, I have a couple of pics, that explain."Straight pins" makes it ezer too.

Just starting to get cool down here. This is how we continue to drive this "willy", toasty heat too. Won't be long, i'll be puttin' it on!

The medic
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Thursday, December 10th, 2020 AT 8:40 AM
Tiny
BKM48198
  • MEMBER
  • 10 POSTS
The fusible link has been checked, .5 ohms resistance, also it is on the wire that feeds the voltage back to the battery and it worked fine after connecting battery voltage to the Y/W wire.
Your wiring diagram is great, it's a smaller version of what my Chilton shows, the 1st diagram I was going off showed 2 fusible links but that was for a 91 Ranger. The older vehicles without all the electronic sensors are so much easier to diagnose problems on if there was an electrical problem, the alternator did 1 job and had a voltage regulator apart from the alternator. I have not unhooked the battery for over a couple of mins, that is a good idea that I had not thought of, I'll do that in the morning and see if it helps, computers help with fuel economy but are a pain when a problem occurs, give me points and a carb to work on instead!
I didn't spend much time on the truck today, just enough to find where the problem was and made sure the alternator would work, I had other things that needed to get done, I'll check it more tomorrow and either get things working thru the OE wire or run a new wire with an inline fuse.
Covered up that would not be bad in the cold weather, looks like a good heater!
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Thursday, December 10th, 2020 AT 8:40 AM
Tiny
BKM48198
  • MEMBER
  • 10 POSTS
Just to show I do know a little bit about working on vehicles here are some pics of my sons car, it started off as a 87 4cyl. Mustang and we turned it into a GT body with 5.0, 8.8 rear end. The black one is my 90 GT, bought new in 89. Just finished his last spring.
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Thursday, December 10th, 2020 AT 8:40 AM
Tiny
BKM48198
  • MEMBER
  • 10 POSTS
It is Grabber Blue with Clear, my son does paint and body at Collex collision so he knows more about the paint than I do, he paints as a side job also, had a Cadillac he painted at AutoRama in Detroit.
Simple things like the 1 wire make finding problems easier, now everything being made is too complicated, I like 60's and 70's vehicles to work on, back before all the electronic sensors.
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Thursday, December 10th, 2020 AT 8:40 AM
Tiny
BKM48198
  • MEMBER
  • 10 POSTS
I tested the voltage at the fuse (15a) and found it had 12v when running, so I followed the Y/W wire back looking for any problems and found a small green spot on the casing of the wire, so I bent the wire a bit and the corrosion started flaking off, seeing that I knew I had found where I was losing the power, the wire was almost corroded thru, still held enough to pass voltage with no load but not loaded. After cutting the wire and stripping it back I used a crimp together wire connector and the alternator was back to running thru the OE wiring. Battery light off, battery charging, no more problems. Till next week. LOL Thanks with all the help, I had been getting frustrated with it.
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Thursday, December 10th, 2020 AT 8:40 AM
Tiny
BKM48198
  • MEMBER
  • 10 POSTS
I don't have a lot of pics of it on my laptop, here are a few. That is a nice color, and a color that is not on many Fox body Mustangs, part of why he wanted it.
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Thursday, December 10th, 2020 AT 8:40 AM
Tiny
KENT46725
  • MEMBER
  • 11 POSTS
  • 1994 FORD RANGER
  • 147,000 MILES
Still having the same problem with alternator not charging battery. Unplugged the instrument panel, thinking it was faulty because gauges are not working. Pulled one fuse at a time while using multimeter to check for short. I'm not getting any return charge voltage back to battery. Alternator has now been checked twice and tests good. Battery is new. I've traced wire that I was told by a ford tech that is the return feed from the alternator to the battery. Odd thing. It reads the same voltage as my battery, not the 13.2 to 13.8 that it should. I am running on the battery which isn't going to last much longer. Please help!
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Thursday, December 10th, 2020 AT 8:41 AM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
Test the voltage at the main terminal of the alternator with the key OFF? What is the voltage?
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Thursday, December 10th, 2020 AT 8:41 AM (Merged)
Tiny
KENT46725
  • MEMBER
  • 11 POSTS
Starting voltage was 12.4, after driving it for 2 days it has dropped to 11. I am getting the same voltage at the alternator main as I get at the battery.
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Thursday, December 10th, 2020 AT 8:41 AM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
That's not what I asked to to test.
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Thursday, December 10th, 2020 AT 8:41 AM (Merged)

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