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Q: Door & trunk ajar, brake and battery warning lights come on while driving off and on. Alternator tested good & bad.

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Head lights go dim when all warning lights come on. Stopped at gas station. Car wouldn't start. Battery was dead. Battery tested good. Alternator tested bad at autozone but good at advanced auto. Can an alternator "not charge" intermittently?

My car has 225000 miles.
My car has an automatic transmission.

A: Hello. Have you had the vehicle scanned for...

Hello. Have you had the vehicle scanned for diagnostic troubleshooting codes? You may want to have the vehicle scanned when you receive these warning lights. They may give you more insight to what the computer has detected. If the alternator tested bad even once, you should replace it. It is possible to get a false negative and a false positive on those tests. You may want to have it tested a third time by a technician. They do not use automated machines, but use a voltmeter and test it on the vehicle. Typically if the alternator works intermittently then the wiring connections are not solid. Check the vehicle's connections and make sure they are clean, dry, and tight. A faulty battery can also cause these issues. Retest the alternator and the battery, and instead of bench testing them, have them tested in the vehicle.

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