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Discussion Starter · #1 ·
Ok this is my old post: Original Thread http://www.gmtruckclub.com/forum/showthread.php?52494-Alternator-issue

So tonight on my way home I noticed my light dim a little, so I looked at the volt meter gauge and it was dipping below 14v where it usually sits and when I accelerated more on the freeway it would dim the lights more. I think its a alternator issue, has anyone had this issue before? I think tomorow I am going to pull the alternator out and have it checked at the local parts store.

Ok so I took truck to the parts store to have the whole system checked and it all checked out ok. I dont know what to do now because after a few hrs I came out of another store hopped in the truck and driving through the parking lot the volt gauge was way under 14v for awhile then it came back up. So now im lost and any advise will be greatly accepted
Now heres whats happening now and a little video to show. The lights also still dim a little and fluxuate at idle. PLEASE HELP ME

http://www.youtube.com/watch?v=UalJb9SSJso
 

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Charging Problems

Have you looked into the condition of your battery ?

Another possibility is the battery cables, corrosion at the battery terminal or
down inside the insulation.
A loose cable can cause reactions of this type. It makes a high resistance contact
if it's not tight enough. This applies to both ends of the cable.

Boneyfingers
2003 GMC Yukon XL Denali
1997 Chevy c-3500 CC Dually
1994 GMC K-1500 Long bed
1994 Chevy K-5 Blazer
 

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Discussion Starter · #4 ·
Boneyfingers the battery tested good and I also checked the cables and they seem good there is no corrosion at the terminals. its tight at the battery and at the starter the negatives are tight as well.

SkullMountainRider there is no aftermarket stereo or anything else to draw current. the replacement alternator is 130amp
 

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Charging Problems

Chris, Since al the usual things check out it now has you
checking the small wiring off the alternator ,, the plastic connector that
puts the voltage to the field windings can have the pins pushed up and
you won't be able to see it without examining it.
Also, an alternator has to have a minimum of 8 volts in the battery to
activate the field windings. There is no magnetism inside the alternator
without the 8 volts, they do not have permanent magnets.
Good Luck,
Boneyfingers
 

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Man, that issue looks like a corrosion issue to me
Make sure Battery terminals and wires are clean.....and that the insulation is not worn down anywhere that would allow for the wire to short on the chasis somewhere.

Get a digital volt meter as well and start checking your voltage readings across the charging circuit. Maybe then you can see if there is a drop occurring at some point in the circuit.
 

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Discussion Starter · #8 ·
Tonight I will chase down some wires to see what I can find and make sure the grounds are good, also i checked the voltage output at the alternator and it puts out 14.4v and then at the battery it reads 14.0 that was just at idle
 

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I just got my 99 Suburban back from the shop yesterday for the exact same issue. I asked the guy who fixed it what he did. He said there was a high amount of resistance between the alternator and the battery. This causes the alternator to work harder and then it will "quit" for a bit and then work fine again. i am guessing the problem gets worse the longer you drive.
So basically he said he cleaned up the connections between the battery and alternator and got the resistance back down to an acceptable level. It would be good for you to have a ohm meter to check out the readings yourself.
I messed around under the hood on and off for about a month before I gave up and took it in to be fixed. All seems to be good now.
Hope that helps.
 

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Has anyone else had this problem? I posted earlier and said mine was fixed. The problem came back, and after more months back and forth to the shop the problem is still not fixed. The guys working on it said they were baffled and gave me my money back. The problem has gotten so bad that I can't even drive the truck anymore. Under ANY acceleration or load all charging disappears and battery light comes on.
BigChris, did your problem get fixed?
Any help here would be appreciated...
 

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Based on what you wrote, I would say look for broken wires, wires where the shielding has worn down, or any kind of corrosion build up....
Corrosion can cause an inverse result....
So ramping up in voltage will result in more resistance being generated which will kill the voltage going from your alternator to your battery.

If you tested all the major components and they test good....then you will most likely have to start tracing out your wires.
The charging system is a rather simple loop, so start checking there.

But do check your various wires for bare wires that could be grounding out on the frame.
 

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So after 3 mechanics (I am horrible with electrical) I finally really got the problem fixed. He used a wiring harness bypass to find the faulty part of the harness. Then traced and found the broken wire. He was able to replace just the broken wire. Still cost me over $700, but it took him over a month of working on it to find.
 

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Question, has the engine been out of the truck? I have solved blinking light problems and fluctuating charge on several gm vehicles. Problem. Those little braided cables and short black wires that go to different panels from the engine are there to provide a good ground. If they are broken or left off you may have these problems. Also many gm vehicles have a short black wire that goes from the neg post on battery to the fender. If you have have a voltmeter, with the motor running and lights on check from NEG bat post to several different places on fender panels, firewall etc. If you get ANY reading there is at least one of these ground connections missing. You can also use one of the test lights with the ground clip on end of wire. connect clip to NEG post of battery and again check several places in engine comp. several fender panels etc. if the light lights you are getting current flow due to a bad ground somewhere. THERE SHOULD BE NO CURRENT BECAUSE ALL THESE SPOTS SHOULD BE GROUND AND AT ZERO POTENTIAL. Your system is depending on ground where fender and other panels are screwed together and due to rust or corrosion you are not getting a good ground. The computer systems are very likely to have problems because they depend on a GOOD POSITIVE GROUND. Before you start making these checks notice if your lights are flickering, if not you may not get a voltage reading. SO BEST to make checks while lights or gages are fluctuating. good luck.
PS seems that when some mechanics ??? take engines out they throw those useless braded straps and those black short ground wires away or just forget to reconnedt them.

You can also make up a lead with aligator clips on both ends and connect it from the NEG batt post to several differend places (grounds) to see if this fixed your problem.
 
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