For my 2017 Mustang GT and am getting a "Service Charging System Now" but only intermittently when on track. Back in the pits and drive home, no issues.

Can the stock alternators withstand the regular redline RPMs of track use? I normally rev to near red-line and hit the rev limiter occasionally each session. Had to end my last session at Dominion raceway early due to this and a engine misfire code.

For a bit of background, I had a similar problem a couple of years ago that turned out to be an engine wiring harness issue at the alternator connector. I replaced the alternator before I knew it was the wiring so that is "newer". Dealer repaired / replaced the connector and the problem went away. Looks like it is back.

I’ve had this issue with my 16 GT350. I replaced the battery 1st. Went away and came back relatively quickly. Changed alternator and it lasted within a week of a year. Replaced harness & battery at the same time. Bench test the alternator & everything seems to be in check. After I did that I had the issue come back after two track events. The nut on the alternator backed off and would intermittently pop up. Finally the nut backed off and the cable was just loosely on the alternator. Since, I was in there I replace with a spare NIB alternator with a larger pulley. After all said and done. I haven’t had any issues in 10 months. After every track event I check the voltage data and it’s been doing its job. If you’d like more detail we can chat offline.

From my experience, the stock alternator (on GT350) cannot take regular Redline RPMs. The pulley is too small and the alternator spins up too much.

The GT could be different but I wouldn’t think so.

Happened on my R (24k mi) but not on my GT (85k mi) - both cars have extensive track use. Went through a few batteries on the R before realizing it was the alternator. I’m assuming it’s from the higher vibration on the Shelby’s than the GT’s and the higher red line likely doesn’t help.

Red Yeti Racing said:

Happened on my R (24k mi) but not on my GT (85k mi) - both cars have extensive track use. Went through a few batteries on the R before realizing it was the alternator. I’m assuming it’s from the higher vibration on the Shelby’s than the GT’s and the higher red line likely doesn’t help.

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Power Master identified that the GT350 pulley is too small and the alternator RPMs are too high at track engine RPMs. I have one of their test units to reduce the RPMS by about 30% and thus far no issues.

Even if you bought their upgraded GT350 alternator with the stock sized pulley the RPMs were burning up their units. This was how they identified the weak spot. (at least thats what I was told from a Power Master rep). I'm not sure if they are selling the pulley yet or not. Their website hasn't been updated in years. You would need to call or email Ed and ask.

Thanks everyone for the inputs! Sounds like the stock alternator is not the culprit so I will need to take a close look at all the wiring in the harnesses to make sure there are no weak links there. Charging over the last several months has been solid so I still have confidence in the alternator. The battery terminals have been cleaned and tightened, so no issue there. I have seen a few, random, brief "Service Charging System Now" messages over the last several months leading me to suspect the wiring in the harnesses but no idea what the trigger is.

If the wiring all checks out, I will look at a new alternator with a larger pulley to slow the alternator a bit (10%? 20%). Hopefully, this does not pose too much of an issue for a daily driver.

2018 200amp and Have the charge issue. New battery, new 3 pin. Single nut tight and stays tight. Bought used alternator same codes po620/p65b guess its time to look at a pulley…$500 for fords alternator seems excessive expense when its charging and communication is happening.

RBELUN said:

2018 200amp and Have the charge issue. New battery, new 3 pin. Single nut tight and stays tight. Bought used alternator same codes po620/p65b guess its time to look at a pulley…$500 for fords alternator seems excessive expense when its charging and communication is happening.

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See my previous post. It has been addressed.

well found my issue for the intermittent Service Charging System Now....with only p0620 and p065B codes that also came and went and no other codes. So I hooked up ODB2 scanner and looked at the Gen Com% and Gen Mon% graphed. Seems an erratic Gen Com% is a bad thing. It should be staggered peak plateau as seen when scanning old unit with no light vs new unit no light on. Just incase someone else has similar issue.