Alternator not charging

Tiny
RYUGAIDEN05
  • MEMBER
  • 1999 CHEVROLET S-10

I was helping my dad replace his alternator on his 99 Chevy s-10 yesterday and we had some confusion on the wiring connections on the back of the alternator. There are three wires down there. I know the one with the rubber boot is secured by the lock nut, but where do the other two go. We got everything connected once, and when we tried to start the truck it would not, so we pulled everything back off and saw that we had a wire connected wrong. Once that was connected correctly, the truck would start. However, it will not charge the battery at all. Is there something we have wired backwards or could it be the battery. We are stumped at this, and we are trying to get it fixed ourselves versus a repair shop.
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Sunday, January 24th, 2010 AT 7:46 AM

26 Replies

Tiny
JDL
  • EXPERT
Hi, my info showed this for S10 four cylinder alternator wiring diagrams with a guide to help you test it

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

Check out the diagrams (Below). Please let us know what you find. We are interested to see what it is.
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Sunday, January 24th, 2010 AT 3:49 PM
Tiny
RYUGAIDEN05
  • MEMBER
Thanks, so it looks like from that diagram we have everything hooked up correctly. I took the battery and had it charged today, now the gauge is showing 12 volts on the dash. However, it does not move up any further while I had the truck running.
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Sunday, January 24th, 2010 AT 6:14 PM
Tiny
JDL
  • EXPERT
Engine running, take a reading at the alternator bat terminal. What is the reading?
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Monday, January 25th, 2010 AT 9:22 AM
Tiny
RYUGAIDEN05
  • MEMBER
My dad carried it to a repair shop today and they said it was some fuse was blown that was causing the problem. Picked it up today and the service engine light came on later. Now he is going to get that checked out.
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Monday, January 25th, 2010 AT 9:36 PM
Tiny
JOHN541
  • MEMBER
  • 1996 CHEVROLET S-10
  • 2.2L
  • 4 CYL
  • 2WD
  • MANUAL
  • 140 MILES
My S 10 has a new battery and a alternator that checks out at Autozone as charging. All connection are good and clean plus tight. From what I have seen everyone is saying to check the little brown wire that plugs into the alternator for a breakage or bad connection. That is if the vehicle has a light for the battery on the instrument panel (gauge cluster). Well mine has no light at all in has a volt meter gauge. Do you still check this in the same manner as the light? And does the charging system go through the the PCM to command the alternator to put out?
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Friday, April 26th, 2019 AT 5:57 PM (Merged)
Tiny
HMAC300
  • EXPERT
Check the three things in pic that I have pointed out and yes still check the brown wire for a bad connection. But the fusible links should have same voltage both sides and not just one or two strands connecting them
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Friday, April 26th, 2019 AT 5:57 PM (Merged)
Tiny
CSEMRADGO
  • MEMBER
  • 1999 CHEVROLET S-10
  • 145,000 MILES
My battery light came on this morning, so I had Auto Zone test and recharge my battery. Everything is fine there. They said it is probably a problem with my alternator, and I should do some more testing before I have it bench tested. My question is this: what tests should I do on it? Also, my fuel gauge is now stuck 180 degrees from empty, and it's stuck there. What should I do about that?
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Friday, April 26th, 2019 AT 5:57 PM (Merged)
Tiny
CARADIODOC
  • EXPERT
Use an inexpensive digital voltmeter to measure the battery voltage while the engine is running. It must be between 13.75 and 14.75 volts. If it's low, suspect the generator. It is real common to go through four to six of them on GM products, after the '86 models, in the live of the vehicle. To reduce the number of repeat failures, replace the battery at the same time as you replace the generator. As they age, they lose their ability to dampen and absorb the huge voltage spikes the generators produce due to their design. Those spikes can destroy the internal diodes and voltage regulator leading to the repeat failures, and they can cause running problems due to interference with computer sensor signals.

Here is a guide to help

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

The fuel gauge should find its way to the proper position when you fill the tank. It looks for the shortest way to the desired setting and that might currently be clockwise against the stop.
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Friday, April 26th, 2019 AT 5:57 PM (Merged)
Tiny
CSEMRADGO
  • MEMBER
After testing the battery with a voltmeter, I can tell the battery is not charging because it has roughly 11.6 volts when the engine is running. Next test?
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Friday, April 26th, 2019 AT 5:57 PM (Merged)
Tiny
CARADIODOC
  • EXPERT
That was a test done many years ago by people who didn't understand how these simple systems work, and it was done on cars with no computers. Many cars today with perfectly good generators will stall when the battery cable is removed. Also, with one shorted or open diode inside the generator, the engine will still run but you will lose two thirds of the generator's rated capacity. You need a load test and a ripple test to find that. The battery is the key component in helping the voltage regulator control system voltage. Every year I did a demonstration for my students on what can happen with no battery in the system. It is REAL easy for system voltage to exceed 30 volts. That will destroy the internal diodes in the generator, any light bulbs that are turned on, and a number of computers. Use the voltmeter. You can find perfectly good ones at Harbor Freight Tools for $4.99.
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Friday, April 26th, 2019 AT 5:57 PM (Merged)
Tiny
CSEMRADGO
  • MEMBER
So I checked the voltage. 12.8 engine off, 11.6 engine running. What now?
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Friday, April 26th, 2019 AT 5:57 PM (Merged)
Tiny
ERICDE
  • MEMBER
  • 1997 CHEVROLET S-10
Electrical problem
1997 Chevy S-10 4 cyl Two Wheel Drive Manual

So I performed the "backyard" alternator test by starting up my truck followed by pulling the negative battery cable. It continued to idle after the disconnection, however, I turned the headlights on and the engine stalled. Should that have happened or should the alternator be able to run the truck and headlights while still providing some extra to charge the battery? My main problem is my battery is dead only on the mornings after i've driven my truck with the headlights on. Any thoughts or suggestion?
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Friday, April 26th, 2019 AT 5:57 PM (Merged)
Tiny
BMRFIXIT
  • EXPERT
Do a battery drain test

Battery drained in the AM only its not an alternator and most likely something is draining the battery over night
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Friday, April 26th, 2019 AT 5:57 PM (Merged)
Tiny
KEN L
  • ADMIN
It sounds like the alternator has gone bad I would replace it with a rebuilt unit. Here is a guide that will give you an idea of how to do the job.

https://www.2carpros.com/articles/how-to-replace-an-alternator

Use 2CarPros anytime, we are here to help. Please tell a friend.

Cheers, Ken
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Friday, April 26th, 2019 AT 5:57 PM (Merged)
Tiny
ERICDE
  • MEMBER
Thank you for the suggestion I just checked out the section on testing a battery and will be trying that right now.
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Friday, April 26th, 2019 AT 5:57 PM (Merged)
Tiny
BMRFIXIT
  • EXPERT
Good luck
let me know
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Friday, April 26th, 2019 AT 5:57 PM (Merged)
Tiny
ERICDE
  • MEMBER
So using a multimeter I did a surface voltage check, 12.73. Now when I connect the meter between the negative cable and the negative terminal it reads the same, did I do the test right?
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Friday, April 26th, 2019 AT 5:57 PM (Merged)
Tiny
BMRFIXIT
  • EXPERT
Also you can use a test light to connect the same way and watch the light to go dimmer as you pull the fuses and look for what is causing the drain
Start pulling fuses make sure that the door is closed and or the door switch is off
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Friday, April 26th, 2019 AT 5:57 PM (Merged)
Tiny
ERICDE
  • MEMBER
I set up a test light and began pulling fuses but the light never dimmed. I traced the negative cable to the engine block and didn't see any corrosion. I've been disconnecting the ground while parked for a few weeks now and had the time today to try figuring it out. Would a full draw or bright test light mean that its grounded out somewhere?
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Friday, April 26th, 2019 AT 5:57 PM (Merged)
Tiny
BMRFIXIT
  • EXPERT
Bad ground will not cause a draw
Defective radio would if have an electrical door locks, stuck actuator would light on in the trunk would defective diode in the alternator would
The reason for the battery is draining something is staying on
Have to locate and find
Key off and all accessories off
If need to access the inside of the car make sure door switch off and not turning the inertial lights on Light should dim when to almost go out when no more draw and pulling fuses is to locate that circuit
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Friday, April 26th, 2019 AT 5:57 PM (Merged)

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