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Bought an alternator now seems like over a decade ago...well maybe half that time. I went for one of the Ebay uber 100 amp jobs. (I can't remember the company, I don't think it is a BnR.....

Had it installed and later discovered  that maybe these aren't the best for charging/output at idle as their monster output only really starts up at decent spin. 

Well this may be the case with mine. Now that I have my car back from several long hospital stays, the charging light flickers at idle. A tap on the accelerator gives me brighter dash lights and better output from my heater or ac fan...I am not running a 1000 amp radio etc. 

Would a smaller pulley fix the problem, or do I need to check something else? Bad ground, bad regulator? Or just get a new alternator? 

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If your idle is set at factory specs (750-800 rpm)--and that should be checked with a dwell meter that incorporates a tach, as your dash tach may not be accurate--you shouldn't have a dim alternator light with everything off except the engine electrics. 

 

My OEM (and original!)  35 amp alternator on my '69 will only allow the alternator light to come on dimly at idle if I have the headlights and heater blower (the two largest current draws) on simultaneously--and will go out over 1000 rpm.

 

Make sure the ground wire from alternator body to engine block is intact and not frayed at either terminal end.  If that wire is bad (and it should be 10 gauge, as the factory one was) it will definitely affect your alternator output.

 

mike

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It goes off when I tap the gas, but starts flickering again when it drops back down to normal idle. It seems like I am running of battery when it is at idle, mostly when the heater fan is on. I have LED headlights, so there isn't much draw there and I don't see any change in brightness when they are on. 

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42 minutes ago, Vicleonardo1 said:

It goes off when I tap the gas, but starts flickering again when it drops back down to normal idle. It seems like I am running of battery when it is at idle, mostly when the heater fan is on. I have LED headlights, so there isn't much draw there and I don't see any change in brightness when they are on. 

Hmm.

 

:P

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Generally alternators start charging @ 1500 rpm initially. In addition to the voltage, check the amperage on the main positive wire charging the battery. Perhaps your voltage regulator is suspect, or your ground from the alternator to the block or other grounds are not good. Remember, it doesn't put out 100 amps all the time.........

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