I have a 97 Crown Vic P71 (4.6L). My battery light has been popping on and off intermittently for about 2 months. I had the local bozo at the parts store check it out. The battery (5yrs old) has low amps. Supposed to be 850, but it is @ 650 or so. The alternator is putting out 14v. I cleaned the terminals, checked all connections. The light comes on less frequently, but I notice a dip on the gauge when the brakes are applied and the gauge is reading a needles width lower than usual. Do I need a battery or alternator? I plan on a battery before winter, but if an alternator is needed too, I'll do it all at once.
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Replace the battery first!... No doubt it needs that!!... Then drive it awhile to see if light comes back on. Unless this problem can be duplicated at the time of testing... NOBODY can accurately diagnose what the problem is!!! ... Fact!!!! .. More than likely the 5 year old, partially discharged battery is the culprit for this problem anyway as It's possible, it has damaged the alternator/charging circuits.... Good luck with it!!
Hi Davepsycho,
Ford products often have complicated alternators that are very finicky...the regulators in the alternator are common for failing and they often test good under certain conditions and only fail under specific conditions, so they can be a little tricky to diagnose...they are often integrated with the PCM (yours may not be due to the age...I'd have to do some research)...my point is that sometimes they require more in-depth testing than the basic tests that the parts store offers. As far as starting with a battery replacement, that probably isn't the best idea, because if the alternator is indeed faulty, it will most likely damage the new battery. The best solution would be to have a qualified shop/technician do some testing to identify the actual cause of the problem, so you don't waste money changing parts that may or may not be bad.
Note: There is a chance that it may not be a battery and/or an alternator...sometimes it could be a wiring issue (due to mice or other causes) or it could be a PCM...proper diagnostic testing by a qualified technician/shop is the best next step...
