Voltage issues

So i have been having charging system issues since i got my car. 03 cobra. At this point the dyi battery relocation the previous owner did could be the culprit. I replaced the alternator about 1 year ago and ran some new ground cables and it got better. My voltage usually varies from 13-13.5v while idling cold. Once heatsoaked maybe 12.5-13v. Via sct x4.The real issue is with any load, for example putting down my windows with the lights on and a/c on the voltage will go down as low 11.5v. This also happens during wot hits. Should i relocate the battery to the original position? Maybe i need a new alternator? Not sure where to start at this point. Any help would be appreciated. Thanks

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Sounds like the alt you have may be getting ready to crap out.
Do you know if it is a upgraded amp unit or just the stock amps?


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You should see 14 volts on a cold start up. I would second that the alternator not up to par.

What alternator?

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I got a 160 amp alternator from ebay. So probably not the best quality. But even after i replaced the alternator i still had the same voltage issues. Im thinking of just relocating battery to stock position and replacing the alternator with a high quality unit that has an external regulator

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My tuner shows about 0.5v lower than what I measure at the battery with a multi-meter so maybe verify your readings if you can. Also, alternators can have poor voltage regulation so what you are seeing may be "normal" for that ebay alternator. Either way I can pretty much guarantee your low voltage readings are not being caused by the battery being in the trunk because it's the alternators job to regulate the voltage once the car is running.

If you're looking to upgrade, I've heard nothing but praise for J2Fab. Personally I have a Mechman 170a alt and haven't had any issues. It never drops below 13.8v.

I was chasing the same issues when I first brought my Cobra home. Previous owner had a trunk battery before but left all the hacked up wiring. Chased all of that down, went through a few alternator rebuilds, a used oem alt and one supposedly new motorcraft alt. Still had the low voltage issues when fully warmed up and lowish voltage at startup. Have a Mechman alt now and all my voltages are spot on. Try that before ditching the trunk setup.

Tldr: If your wiring is good you need a better than OEM alternator.

Thanks guys. Ill be ordering a new alternator soon

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