Not charging
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New User
Joined: Nov 2006
Posts: 11
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Not charging
I am on my 3rd 7.3 single alternator that is not charging the batteries. Battery light on dash does not come on but tested it and it does work. Battery voltage at alternator same as batteries. Fuse good at battery junction box. Batteries are just 3 years old and had checked at NAPA and tested good. No voltage drain in 10 hrs. Pulled on fusable link on starter relay seems ok. Last alternator battery light came on. Latest alternator battery light does not come on. Worked fine for a couple of weeks, kept checking voltage at batteries. Any suggestion would be greatly appreciated. 70 miles to the closest Ford dealer and will have to rent a car.
Post Fiend
Joined: May 2006
Posts: 10,007
Likes: 4
From: Central Florida
I recently went throught a similar problem. First things first, Use a mutlimeter ground to the alt case and pos to the battery terminal. Check that voltage while running at idle and say around 1500 rpm. You should notice a slight power increase, if not alt is dead. If you do, next step is to leave the pos on the alt and test neg on battery. If the voltage drops, you have a bad ground from the alt case to the battery. Then reverse that so the ground is on the alt case and pos on the battery. If you don't have a close voltage, you have a blown fusible link.
Another test is to charge your battery all the way. Your battery should hold 13.2 volts, if one cell is dead you should have 11.2 volts. My problem was one cell was failing and I couldn't diagnosis until it died and held 11.2 volts max. At that point it was internally shorted and self discharged quickly. If you battery will not take and hold 13.2 volts, replace it.
Another test is to charge your battery all the way. Your battery should hold 13.2 volts, if one cell is dead you should have 11.2 volts. My problem was one cell was failing and I couldn't diagnosis until it died and held 11.2 volts max. At that point it was internally shorted and self discharged quickly. If you battery will not take and hold 13.2 volts, replace it.
