What am I missing?

Mopar&vettedude

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Im currently at a loss. I wanted to upgrade to a 100 amp alt from the factory 65 amp and did that, but for some reason it wont hold a charge unless under a load. I put a volt meter up to it and it only reads 12.6v, bring up the rpms and it just creeps over 13. Are the 100 amp alt suppose to have a ground coming off the body or was i suppose to change to the voltage regulator to match output? Almost considering going back to a 65 amp. Any thoughts?
 

AMC Diplomat

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Someone smarter than me would know better, but it sounds like you need a resistor or a diode or something to excite the alternator so it kicks out voltage. There are years of debates about 100 amp alternators on the A, B, and C body forums. People get really upset and into the weeds about it over there.
 

Aspen500

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The regulator is the same.

The 100 amp alternator needs a ground wire. IIRC, there's a ground stud on it.
 

Mikes5thAve

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It should ground through the bracket like any other alternator but it never hurts to try something simple like that.
Personally I wouldn't bother with the bigger alternator unless you're doing something that needs the extra power.
 

Aspen500

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Double checked and the alternator ground stud is next to the B+ stud diagonally. Wire diagram shows a 6 gauge wire from the grd stud to the engine block. Doesn't say where, just the block.

For whatever reason, the 100 amp doesn't ground through the case to the bracket like the lesser amp alternators.
 

69-

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You can never over-ground...
Although, most of the time (eg non full 100A output) the ground via mounting studs should suffice.

But I guess the engineers did not add that 6Ga ground wire for their pure philantrophy... ;)

Doesn't matter where at the block, but it needs to be a good ground, eg no oil, paint or such inbetween.
 

Mopar&vettedude

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Kind of weird that they built them like that. Makes sense on the no such thing as over grounding. Ill look into the stud and hopefully that should fix it.
 

Camtron

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I run a 100amp, has a ground strap on it. A side note; I go through a decent amount of voltage regulators since putting the 100amp alternator on the car. Like 3 a year. Didn’t happen with the 65amp when it was on the car.
 

Aspen500

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It's best if you use a repop regulator, or a known good original, both made in USA. Most of the parts store ones have cheap internals and, worst of all, seem to all be made in China.
 

Aspen500

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If the crank pulley is smaller than stock and[/or alternator pulley is larger, it may not spin fast enough to charge much at idle.
 

80mirada

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The 100 amp alternator is vibration dampened, so it needs a separate ground. Early cars with it had a ground that ran between the heads as well
 
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