# Altenator light comes on during idle



## ChiefPontiac66 (Jul 12, 2012)

I just started up my 66 Lemans for the first time since last fall. The battery light comes on while it idles, which it didn't do before. If I increase the RPM's a little, it will go out. I replaced the external voltage regulator with a solid state one last fall. I have only ran it a couple times since it was replaced with no problem previously. What would cause this to happen?


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## BearGFR (Aug 25, 2008)

Check the voltage at the battery with the engine idling. It should be very close to 14.4 volts. If it's lower than 13 or so, suspect either a bad alternator or a bad voltage regulator. If you pull the alternator and take it to one of the big box parts stores, they usually have a machine that can test it for you.


Bear


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## Matthew (Feb 11, 2011)

You would not be the first to have a new voltage regulator go bad. If it is the Duralast VR715, 50% (in my estimation) are bad straight out of the box. Matt


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## allpawl66 (May 9, 2008)

Duralast VR715 , never had any troubles with them . Have used a dozen on friends / own cars for years . Good reviews on other sites as well .


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## geeteeohguy (Feb 2, 2008)

I have had this happen due to worn brushes in the alternator. If it's an older unit with a lot of wear, anything is possible. What Mr. Bear said...have it tested.


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## ChiefPontiac66 (Jul 12, 2012)

I checked the voltage at the battery at idle and it only registered at 12.29 volts. Looks like I'll have to have my alternator tested as Bear suggested. It's an old unit so maybe it's bad. Thanks for your help guys.


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## the65gto (Oct 9, 2008)

ChiefPontiac66 said:


> I checked the voltage at the battery at idle and it only registered at 12.29 volts. Looks like I'll have to have my alternator tested as Bear suggested. It's an old unit so maybe it's bad. Thanks for your help guys.


What is the voltage at the rear of the alternator at idle. (Big red wire)


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## ChiefPontiac66 (Jul 12, 2012)

Well, it turned out to be the Duralast VR715 I bought. I had gotten a defective one. After the alternator turned out to be fine, I exchanged the defective voltage regulator for a new one. Now the problem is gone. Thanks for all the help guys!


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## Matthew (Feb 11, 2011)

Right. You might be going through this again in the next couple months. I would recommend moving away from the Duralast VR715. I got it that Allpawl66 has never had a problem with them, but there are a number of people that have had problems with them. Matt


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