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I just replaced both my alternator and my battery but I am still getting that battery light and my mustang will die after driving it down the road. I had the battery tested and the alternator bench tested and everything is supposedly okay? I need some help!!!!!!!
 

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This problem is probably above my pay grade, but:

It sounds like the car is running on the battery and not switching over to the alternator after start up. But it is not clear to me how you are getting the car started in the first place. Are you getting it jumped each time or is it starting fine on the battery?

I would isolate the problem first. Start the car, then unhook the negative cable on the battery. If the the car remains running, then your alternator is fine. If the car stops, then your alternator is the problem.
 

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Don’t mean to step on any toes, and while it worked for 60s cars, do not disconnect the battery on a modern car while it’s running. This will induce a phenomenon called “load dump” and can spike the electrical system with over 100 V from the alternator, potentially damaging modern electronics.

About a year ago a guy had a similar problem as what you describe, ended up being an abraded wire harness. May want to check over your wires and connectors real good. Also, while the car’s running, connect a volt meter across the battery. You should see something around 14 volts or so if the alternator is charging the battery. If everything looks ok by these checks you may want to take a second look at the alternator, as a simple bench test may not show all problems (e.g. open diode).

Load dump - Wikipedia, the free encyclopedia
 

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I agree 100% with stars! I have purchased alternators from autoparts stores that were re-manufactured and took up to the third one before it actually worked! Ford has had issues with alternators for awhile
 
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