Altenator Question


New Member
Sep 22, 2004
New Jersey
About to replace my alternator for the second time on my 2003 V6. Got it tested the other day and its only putting out between 11-12 amps at idle - I'm told it should be doing 14. Sometimes it seems to work fine, but other times when I'm sitting and idling I can watch the voltmeter drop quite a bit and the lights will start to dim. Sometimes it'll drop so much that the Cd player will turn off, the ABS light will come on, and some other lights in the dash....very exciting stuff. But other times, I can leave my car at idle for like 5 minutes and the voltmeter won't move at all. All my research seems to indicate its the alternator, yet again. Does anyone have any other theories.

Either-way, I don't plan on keeping the car much longer and I found a rebuilt alternator (the one on the car already is a rebuild and lasted for about 3 years). I know the stock alternator is 105 amps but this one is 130 but, I'm told it'll fit and function just fine. My question is, is there any potential problems having a different, and more, voltage alternator on the car? Thanks for your help!
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SN Certified Technician
Aug 14, 2009
Houston Texas
Do you have a BIG sound system (or anything needing a lot of current such as aftermarket head lights)?

Do you have under drive pullies installed? Underdrive pullies can reduce the alternator's output at low RPM's.

Has any work been done to the car? What is the condition of the battery? Are the battery terminals clean and tight?

FWIIW; todays car will not run without a strong battery. The battery is needed to excite the alternator field coil. NO battery=no alternator. The days of jump starting a car with a totally dead battery are over.

Remember that a large increase in load can over whelm and collapse the alternator field coil. Once collapsed, the alternator will cease generating electricty. The battery is REQUIRED to re-excite the field coil. If the battery supply is weak, then the process breaks down. The usual symptom is poor voltage regulation (voltage surges up/down or remains low).

It is possible that your problems are from a weak battery or loose connections to the battery, ground, or alternator. Or the alternator just may be bad. Don't cut corners. CLEAN, CLEAN, CLEAN (even the top of the battery).

I am more familiar with the GT. I do not know off the top of my head if the 130 amp alternator will fit the V6. If it fits, it will not cause any problems.


New Member
Feb 2, 2010
Measure your battery voltage at idle speed. voltmeter should read between 14-15 volts. If it's outside these values you may well have a charging problem. If everything is clean & tight,then the problem is in the alternator ,rectifier or voltage regulator. The regulator can be changed, but I believe the rectifier is integral in the units fitted to the Mustang. With everything on & the car at just above idle the alternator should be able to carry the full load from all circuits. The older technology Dynamo would not be able to do that but a modern alternator will produce most ( if not all) of it's current at below 2000 RPM.

The larger 130A unit will not harm anything but make sure the main lead coming off the alternator is up to the job! especially if as mentioned above you have high current auxillery devices fitted like a 600 watt amplifier, sub woofer etc :D