Alternator not charging

Tiny
FACTORYPILOT
  • MEMBER
  • 1990 CHEVROLET SILVERADO
  • V8
  • 4WD
  • AUTOMATIC
  • 175,000 MILES
Alternator not charging. Changed alternator with no change. A+ wire to alternator reads 12.5V with key off. After starting engine, voltage went down to 6V. When I jumper a wire from battery to alt. It works fine. Question where does the red wire from the Alt. A+ terminal go? The tilt steering column was just removed to tighten the 3 bolts that work loose after time. Could this problem be related to that work? I see a purple wire on starter sol. And no red wires on terminal strip on firewall. I am afraid this red wire is loose or has a bad connections somewhere but can't find where it goes. A schematic would be helpful.

I just turned on the key and got the Bat. Warning light with the Volt meter showing about 10 v. When I started the engine the Lt. Went out and it started charging normally. Tried the same thing again with the same results, so now it is intermittent. Thanks for the schematic. Now I think I can trace things out and maybe find the problem.

When I put the cover back on the junction block at the back of the engine bay, (which loads the wires a little) the alternator would not come on line again. Also voltage at the battery was about 12.5 and at the alt. Terminal was 10.7. Thinking I might have a fuseable link that was causing high resistance, I disconnected the battery neg, and was going to check the wire to the alternator for resistance. When I put a socket on the nut it took no resistance to turn it. Turned out someone had once hooked up another lug and wire with fuse holder for a trailer brake or something to the same terminal and had evidently left it slightly loose. All of the other nuts were tight. I cleaned the connections, put a star washer under the nut and tightened it down, reinstalled the cover and it works fine now. Thanks for the wire diagram with color codes.
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Saturday, February 27th, 2010 AT 1:03 PM

15 Replies

Tiny
KEN
  • ADMIN
Hello,

This sounds like a connection problem somewhere in the wiring harness. Here is a full diagram (below) of the alternator wiring that you will need to get the problem fixed.

Also here is a guide to help with the testing, check for power everywhere in the system

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

Please let us know if you need anything else to get the problem fixed.

Cheers, Ken
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Monday, June 12th, 2017 AT 4:34 PM
Tiny
KIMBERLYMAE63
  • MEMBER
  • 1990 CHEVROLET SILVERADO
  • V8
  • 4WD
  • AUTOMATIC
  • 17,600 MILES
Electrical problem
1990 Chevy Silverado V8 Four Wheel Drive Automatic 176, 00 miles

I have replaced both the alternator and the battery and the truck chevy 454 still will not charge. What could it be
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Monday, June 12th, 2017 AT 4:35 PM (Merged)
Tiny
RASMATAZ
  • MEMBER
Check gauges fuse 20amp and charge indicator if okay double check the wiring if it continues get both the alternator and battery load tested
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Monday, June 12th, 2017 AT 4:35 PM (Merged)
Tiny
NATESDOGG113
  • MEMBER
  • 1997 CHEVROLET SILVERADO
  • V8
  • 4WD
  • AUTOMATIC
  • 68,000 MILES
Electrical problem
1997 Chevy Silverado V8 Four Wheel Drive Automatic 68000 miles

I need to figure out why my alternator is not charging my battery. It started out by my radio turning off, then my transmission was shifting hard, then my blinkers did not work then my truck started to stall. And that's in a matter of minutes of each other.

So, here's what I've tried. New battery, 2 new alternators, new negative and positive battery cables (along with the fusible link between the pos and alternator), checked all fuses and relays in both fuse boxes (visually and with dmm), checked continuity of all cables withing the charging system, tested starter at AutoZone(passed), and recently checked both alternator and battery at AutoZone and other than having to get my brand new battery recharged everything checked out good.

I have no idea what to do next and I have spent almost $500 on trying to figure this out.
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Monday, June 12th, 2017 AT 4:35 PM (Merged)
Tiny
CARADIODOC
  • EXPERT
Hi natesdogg113. Welcome to the forum. Start by measuring the voltage on the fat red or black wire on the back of the generator, and the small red wire in the plug when the ignition switch is turned to run. Holler back with those values.

Caradiodoc
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Monday, June 12th, 2017 AT 4:35 PM (Merged)
Tiny
UMSURE12
  • MEMBER
  • 1985 CHEVROLET SILVERADO
I have a Delco 10 si alternator that charged but needed a rotor because the drive end was worn down so bearing was loose. I put in a new rotor that I received from WAI. It would not charge. So I tried a another new one and no charge. I have tried 3 new rotors with no charge. I borrowed a rotor out of a known working alternator just to try it and it charges. I took the "bad rotor and put it in the "known" working alternator and no charge. What gives? Thanks, Jeff
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Monday, June 12th, 2017 AT 4:35 PM (Merged)
Tiny
CADIEMAN
  • MEMBER
U will need to replace the rectafire bridge
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Monday, June 12th, 2017 AT 4:35 PM (Merged)
Tiny
UMSURE12
  • MEMBER
I tried the same thing today, I took a new alternator apart and stole the rotor.I put the rotor from the new alternator, in the not charging alternator and charges. I installed the rotor from the not charging alternator into new alternator that I stole rotor from and no charge. Confusing.
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Monday, June 12th, 2017 AT 4:35 PM (Merged)
Tiny
CADIEMAN
  • MEMBER
WHY DO U KEEP CHANGING THE ROTOR? CHANGING THE ROTOR ISN'T GOING TO FIX THIS. THERE IS ANOTHER PART BAD ALSO. THEIR ONLY 4 PARTS.
ROTOR
BRUSH HOLDER
VOLTAGE REGULATOR
STATER THE ROUND WOVEN WIRING PART THAT THE ROTOR RIDES INSIDE.
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Monday, June 12th, 2017 AT 4:35 PM (Merged)
Tiny
BUBBAKEG
  • MEMBER
  • 1985 CHEVROLET SILVERADO
  • 7.4L
  • V8
  • 2WD
  • AUTOMATIC
  • 73,000 MILES
I noticed the gauge was showing it was not charging so I replaced the alternator and the needle went straight up like it should but as a few months has gone by I noticed the needle was down low again so I replaced the alternator again and still the needle on the gauge is low so I bought a new battery and same thing I also have noticed that my headlights are not very bright there almost putting out a yellow color light. Thank you so much for your time
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Monday, June 12th, 2017 AT 4:35 PM (Merged)
Tiny
WRENCHTECH
  • EXPERT
Stop relying on that dash gauge and measure the charging voltage using a digital voltmeter at the battery with all the accessories turned off. You should be seeing something between 13.8 and 14.5 volts.
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Monday, June 12th, 2017 AT 4:35 PM (Merged)
Tiny
BUBBAKEG
  • MEMBER
Hello again I did that and it says 13.7
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Monday, June 12th, 2017 AT 4:35 PM (Merged)
Tiny
WRENCHTECH
  • EXPERT
Then the system is charging, although a little low and you probably don't have a problem.

Make sure you didn't have anything turned on like lights or AC when you tested that. I would also have the battery tested as it could be the cause of low charging voltage also.
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Monday, June 12th, 2017 AT 4:35 PM (Merged)
Tiny
LINDBLADJEFFY
  • MEMBER
  • 1977 CHEVROLET SILVERADO
  • V8
  • 2WD
  • AUTOMATIC
  • 130,000 MILES
We have a 1977 chevy 1 ton dually with a 454 and have replaced the battery, battery cables and alternator but it still wont hold a charge any suggestions?
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Monday, June 12th, 2017 AT 4:35 PM (Merged)
Tiny
CADAMW
  • MEMBER
I unfortunately do not have a solution for but am pulling my hair out over this same issue with my 1990 silverado. Replaced all of the above just as you have and nada. If and when you find the solution PLEASE update if you would. I will do the same hopefully sooner than later, good luck.
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Monday, June 12th, 2017 AT 4:35 PM (Merged)

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