3rd Alternator, same results


FBA

GT Owner
Dec 5, 2010
1,639
31.022340° N / 44.846191° W
Changed my alternator as the original one was making some noise and voltage was irregular. I could see fluctuations in the lighting in the car, so figured it was time.

We ordered an OEM unit and installed it, but it ended up at 14.8-15.3 volts charging. Ordered a rebuilt and installed that, only to find the exact same thing...

I am told the ECU sets voltage output from the alternator...can anyone confirm and clue me in as to where the issue may be? Car runs fine, but shop is concerned about overcharging. The original alternator read the exact same voltage on my gauges.
 

Xcentric

GT Owner
Mark II Lifetime
Jul 9, 2012
5,019
Myakka City, Florida
Overcharging is >15.5 volts. Normal charging is 13-15 volts. If voltage drop between the alternator and the battery is >0.5 volts, you have a problem in the circuit. Otherwise, high charging rates can be caused by bad grounds (regulator/alternator to engine and/or battery to frame).
 
Last edited:

2112

Blue/white 06'
Mark II Lifetime
Do we have the same alternator as the GT500?
 

FBA

GT Owner
Dec 5, 2010
1,639
31.022340° N / 44.846191° W
Overcharging is >15.5 volts. Normal charging is 13-15 volts. If voltage drop between the alternator and the battery is >0.5 volts, you have a problem in the circuit. Otherwise, high charging rates can be caused by bad grounds (regulator/alternator to engine and/or battery to frame).
So at 15.3 volts, it is not overcharging?
 

PeteK

GT Owner
Apr 18, 2014
1,118
Great Falls, VA
That's too high. How are you measuring it? With a digital meter across the battery terminals or with the gauge on the dash? You must use an accurate gauge across the battery terminals. If that different from the gauge on the dash, start looking for a problem with the gauge or grounds.
 

FBA

GT Owner
Dec 5, 2010
1,639
31.022340° N / 44.846191° W
Multimeter across the battery...
 

PeteK

GT Owner
Apr 18, 2014
1,118
Great Falls, VA
Multimeter across the battery...
Does the gauge agree with the multimeter?