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Discussion Starter · #1 ·
93 Ford mustang GT. 3G alternator. I could drive no prob the voltmeter stays good. I can sit in traffic or red light and the voltmeter (Autometer) will read 10 is this normal or is this the Alternator? Thanks!!!!!!!!!!!
 

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Even if your alternator is not keeping up, the battery voltage should hold it up to at least 11.5 volts. What kind of power accessories are you running when the voltage dips this low at idle? There's a good chance your alternator is fine, but the battery is going bad.
 

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Discussion Starter · #5 ·
no the battery starts the car fine. I have an electric fan Mark 8. It holds about 13 amps with the fan on. With the fan and AC on it dips about 10 volts or I could be driving at nighrt when I don't need the ac and the same thing 10 volts with just the lights and the fan
 

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Take the car to an auto electric shop. They will usually check it out for you for a small fee or sometimes for free.
I think it's your alternator's diode trio that has gone bad.
 

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Ah, ok, the Mark8 fan draws huge current do it doesn't suprise me that the voltage drops that low at idle with the fan running, depending on how it was wired into your system. There's a chance the alternator is fine, just not up to the task of supplying the 40+ amps it takes to run the MK8 fan, heater/ac blower, and headlights at idle. Switching to a higher output alternator like a PowerMaster will probably help a lot... but also increasing your idle rpm just slightly can make a big difference if it's as low as 600rpm.
 
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