1998 Ford Taurus battery light on battery drains overnight

The usual culprit is a light that stays on, so check the car after dark to see if there is anything staying on. That could include a trunk light, so check that as well. If you have added any accessories, disconnect them and see if the problem goes away. So installers run things directly to the battery, which should not be done except for very specific equipment. It is better to have any add ons wired through the fuse panel on a switched circuit so that when the key is off, there is no power is off to everything.

you then have a parasitic drain on the battery , this could be a light left on in the glove box, trunk , under the hood so check round the vehicle for signs of something on that should'nt be on when ignition off.keep me posted if you wish

There are few possible reasons why battery is not holding charge.May be its weak battery or there is loose connection between battery to alternator.There are few troubleshooting help links,related directly to these types of problem,with there troubleshooting procedure.--------Click the link below and go through its troubleshooting details to resolve the issue:---Car battery loosing its charge overnight? http://schematicsdiagram.blogspot.com/2011/11/car-battery-loosing-its-charge.html
--------How to troubleshoot car battery?

http://schematicsdiagram.blogspot.com/2011/06/how-to-troubleshoot-car-battery.html

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After replacing Alternator, the battery indicator light Comes ON dash? http://howtobyme.blogspot.com/2011/11/after-replacing-alternatorthe-battery.html
----------1998 Ford F150 pickup Battery Drains overnight due to Alternator? Alternator drains car battery? http://technoanswers.blogspot.in/2012/02/1998-ford-f150-pickup-battery-drains.html---------- 2002 Ford Focus sits over night and battery goes dead? http://technoanswers.blogspot.in/2012/02/2002-ford-focus-sits-over-night-and.html----------- Charging system problem on Chrysler LHS car? http://technoanswers.blogspot.in/2012/02/charging-system-problem-on-chrysler-lhs.html
-----------Toyota Corolla: Battery Drains out? http://howtobyme.blogspot.in/2012/05/toyota-corolla-battery-drains-out.html--------- 1999 Ford Taurus: Battery not holding Charge? http://whoisbyme.blogspot.in/2012/06/1999-ford-taurus-battery-not-holding.html
-------------How to Inspect Car battery? http://repairhelpcenter.blogspot.com/2011/12/how-to-inspect-car-battery.html------------ How to Test Car Battery? http://repairhelpcenter.blogspot.com/2011/12/how-to-test-car-battery.html--------- Car Battery Servicing? http://repairhelpcenter.blogspot.com/2011/12/car-battery-servicing.html--------- How to Replace Car Battery? http://repairhelpcenter.blogspot.com/2011/12/how-to-replace-car-battery.html-------- How to Inspect Car battery Terminals? http://repairhelpcenter.blogspot.com/2011/12/how-to-inspect-car-battery-terminals.html---------- How to clean car Battery terminals? http://repairhelpcenter.blogspot.com/2011/12/how-to-clean-car-battery-terminals.html---------- How to Replace Broken Car Battery Cables? http://repairhelpcenter.blogspot.com/2011/12/how-to-replace-broken-car-battery.html
--------------These details and procedure will help.keep updated for more help.Thanks.

nancycmixon, When you see this "check your charging system" you need to have the alternator checked. This is the main component for the charging system. A normal alternator will put out 13.6 to 14.6 volts. A few tenths of a volt either way won't mean too much but if they are extremely over or under these values means you have a bad alternator. I believe that your vehicle has a voltage meter in the dashboard and it will usually read in the thirteen to fourteen volts range. As far as your battery losing its charge overnight means that you have another problem and that is you have what is called a parasitic drain. There are a certain amount of parasitic drains already in the car with the radio memory and maybe a clock that constantly displays the time and the antitheft system in the car. These will not drain your battery overnight. You have something else draining your battery that is your problem. Have the alternator checked and mention the battery drain. There is test for this but it is too lengthy to post here. Sorry about that. Good luck with this.

I fixed the same problem in my 1990 Ford Taurus, it turned out to be the external voltage regulator.
I determine that my external voltage regulator had failed by testing the charging voltage across the battery while the car was idling. It should be a maximum of 15V for most batteries; mine was at 17.8V which means the voltage regulator was not regulating the voltage sent to the battery. Also when the car was parked it pulled a constant 3.0 amps (which drained my battery overnight). I was able to test for the amperage draw by just disconnecting the voltage regulator and hooking up my multimeter in series with the battery, the draw was gone.
I replaced the voltage regulator, which is a very easy fix, and I was good to go again. :)
Hope this helps someone too.

Sounds like a bad brake light switch. It's mounted on top side of your brake pedal. Domelites are a faulty door switch. Both are fairly inexpensive repair, local parts store should have everything easily in stock.

You obviously have a short. I think it may be your starter selinoid or starter relay. It could also be a mercury switch failure in your trunk or under the hood. They turn the lights on & off accordingly under the hoods. Have your starter checked out. Also it could be an ignition switch problem. Check the starter first. Good luck!

you should check the alternator to see if it is putting out the voltage it should. (13 to14 volts) If not the car is draining the battery until it quits running. putting the lights on would just speed up the process

Something is draining it when it is off. Check lights under hood, in trunk, glovebox, power door locks, amateur installed stereos, GPS, sound boosters, anything else which is or could be running when ignition is off.

Sounds like something is shorting out but first I would not trust that the battery is good . So try unhooking the battery after its been charged and then hooking it up the next morning to see if it will start your truck and if it works the battery is good and need to find the short but if it is drained and dont start truck its a bad battery.