Lights dimming with HO alternator [Archive] - Forum


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04-14-2006, 09:05 PM
K to start it off, I have done some searching and found nothing that would really apply directly to my question. I just installed a new High output alternator from Mr alternator and upgraded the wiring to a 4 gauge cable. My issue is I notice as I idle the power level goes down. My headlights dimm about a 1/4 and the car idles a little rougher. I have gone for a few longer drives and had no issues when the engine runs at about 1200 RPM+. My question is, does the High output alternator put out less power than a stock alternator at lower rpms? Does anybody know the amperage of the ( MR ALT. HO alt ) as compared to a stock alternator. just to add a bit of info. My battery is a redtop and it was tested last week and levels are fine. I have checked the wiring and no issues there. My car normally idles at about 650.

Why do my lights dim on idle? isn't a H.O. Alternator supposed to match or succeed the idle output of a stock or is it only at higher RPM's is puts out more?

Mike Jung
04-14-2006, 09:10 PM

The HO alternator needs more rpms to produce current.
Made for 800 rpms & up.
Our GA idles at 650.

You need a smaller alternator pulley; so the alternator spins faster.

Edit: Oops, that was an Ohio Generator HO alternator.
Ohio Generator problem (

04-14-2006, 11:03 PM
Agreed ^^^ Try that first... The smaller pulleys should run < $20

04-14-2006, 11:22 PM
3 years later and I finally understand why my car does that. LoL...solves that problem.

04-15-2006, 11:17 AM
Makes perfect sence. Thanks guys.

I do have another question. Where can I pickup a smaller pulley? PFYC has a lighter one, but aside from going to a shop, are there any online sites that offer pulleys that are smaller than the 2" diameter stock/Mr alt pulley?