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Old 02-26-2012, 09:29 PM
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known good alternator not charging

okay, so i have an 81 chev 1/2 ton 2wd with a 73 350 in it. my alterantor wont charge now. when i start it the voltage sits around 11.9 at idle then with i rev it a bit its jumps to 12.6-12.8 and holds there and then if i rev it higher and hold the throttle it'll charge around 13-13.2. i have swapped it with two other known good alternators and its the same EXACT readings... brand new belt and they are all the 3 wire internally regulated... my trans was having issues so i trailered it to the shop and i got it back friday night and it seemed fine then saturday night i was taking my gf home and all of a sudden my stereo died and by the time i got home i could see better with no headlights because they were so dim on bright that my eyes had adjusted to the darkness. i noticed my alt belt was inside out when i got home and the belt was pretty worn so thats why i bought a new one thinking it was just that stupid belt slipping and when i replaced the belt it charged at 13.8-14.1 and i drove it around this afternoon i was gone for three hours running various errands and then again i went to the barn to say hi to my lady and the radio died and i checked the voltage and at idle i was sitting at 12.7 ( i personally think my truck is now jealous of my gf and is mad at me for taking it to a shop lol)

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Old 02-27-2012, 03:58 AM
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By known good, I assume you took it and got it tested, if that's the case ..... sounds like a belt slipping. Do you have surp belt or the old V groove
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Old 02-27-2012, 07:13 AM
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I have the v-belt, and it's cranked down as hard as I can get it. Another thing I noticed is my alternator light no longer comes on. When I turn the key on before I start it, it should be on but it's not and I replaced the bulb with a new one even and it still won't come on
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Old 02-27-2012, 08:36 AM
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Check the fuses to the gauges
That lamp is tied to the instrument panel wiring.

If the does not come on with the key on---try this:

Unplug the 2-wire connector from the alternator and ground the wire
that is either brown or white (NOT THE RED ONE) to the engine.

If the light comes on----there is something wrong with the alternator
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Old 02-27-2012, 11:10 AM
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I put it on a trickle all night so I could get to work this morning and noticed my light came on when it should have and I was charging 14.2 then I checked again afteri got to work ave it was still charging good
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Old 02-27-2012, 04:25 PM
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If it happens again run a temp jumper from the large lug to the #1 terminal on the alt, that'll provide the 12v needed to excite the alt, check you output if it's 14+ ..... you have a short somewhere between the connector and the idiot light or from the idiot light to the 12v source.

Wouldn't recommend leaving it like that tho" if it doesn't shut off when you turn the key off you'll have to pull the jumper.
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Old 02-27-2012, 04:35 PM
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I just fixed it, there was a wire rubbing on my column in the engine compartment and it had worn a small hole in the insulation and it was grounding out. Replaced it and now I have no issues thanx for all the help guys
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Old 02-27-2012, 06:01 PM
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Good to hear you got it figured out
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