battery light 99 grand marquis

Asked by Oct 09, 2014 at 11:31 AM about the 1999 Mercury Grand Marquis 4 Dr LS Sedan

Question type: Maintenance & Repair

battery light started coming on intermittently have 12 volts when off and 14 when running

2 Answers

116,235

So it is either the alternator getting ready to fail or you have a wiring problem somewhere in the charging circuit. Make sure the alternator and engine grounds are good first as this seem to be a problem area as the car gets older. If you don't find a problem with the wiring then take it to someone who can check the system on the car, they can actually load the system to see if the output is within specs.

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400

Hope you checked when light was on. If you have 12 volts engine off (normal) and 14 volts engine on (normal) at least you know battery is being charged like it suppose to you won't be left dead in the water. I think it's in the alternator itself because the alternator is what turns on the light I think it's got a bad diode inside the alternator which is turning on the light.

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