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First of all, the battery light never means that you have a bad battery. You COULD have a bad battery, but that is another issue apart from the battery light. The battery light means that the regulator in the alternator doesn't see a charge going to the battery. That doesn't mean you have a bad alternator either, but you could have a bad alternator. The light is turned on by the regulator which is built into the alternator. Just because you have had the alternator checked does not mean that it is good. For one thing, I have seen a lot of alternators that were working, but there was a problem with the regulator falsely turning on the light. Guess what? The fix is replace the alternator, since the regulator is part of the alternator. Also, it is possible that you have an intermittant problem in the alternator. That is consistant with the battery light going on and off. If the alternator is charging at times, and not charging at other times, it may just be that the alternator is bad but it was working at the time they checked it. Another possibilty is that you may have an intermittant problem in the wiring to the alternator. The alternator requires a field voltage supply to it in order to work. If the field goes away, the alternator stops charging. You could have a break in a wire going to the alternator that is making contact at times, and not at other times. Most likely that would be right at the alternator connector itself, that is where I usually find problems. There are two connectors, one has three wires, the other has one wire. Try tugging a little on each individual wire as it enters the connector hardshell, and see if you find a wire broken inside of the insulation.

I've seen cases where the belt was slipping on the alternator and the battery light would go on, then off. It was caused by a worn belt or the belt tensioner itself was bad. Check those things first before replacing an expensive alternator.

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โˆ™ 2012-07-25 00:33:26
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Q: Why would the battery light come on and go off you replaced the battery and had the alt checked and its OK 1998 Grand Marquis?
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