My 1999 mercury grand Marquis us killing my battery. So is it the battery or the alternate?
Test alternator output voltage. It should be 14.5 volts or so. If not it's probably bad. Does it drain down while driving or when it sits overnight? If while driving check alternator and battery connections. If overnight test for parasitic draw.
www.youtube.com/watch?v=zdIKNnwEjIs -- this is how to do the draw test.
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