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Q: My 1991 Mercury Cougar LS has a replaced alternator and new battery but it seems the battery dies over night and the car will not start.

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My 1991 Mercury Cougar LS has a replaced alternator and new battery but it seems the battery dies over night and the car will not charge. Can anybody please help me to pinpoint and fix the problem?

My car has 180600 miles.
My car has an automatic transmission.

Hi there. It seems that there is a Parasitic Load on your battery. This is a load of something on when the key is out of the ignition switch and the doors shut. To check this condition perform the following:

  • Remove the negative (-) battery cable from the battery
  • Take a digital volt meter and put a lead on the negative (-) batter cable and the other lead on the negative (-) battery terminal
  • With seeing the meter, get in the cab with the doors shut, turn on everything one thing at a time

When the meter reads 0 or near 0 volts, then that item that was operated is shorted out and causing the battery to have a load on it when the key is not in the vehicle. It is normal to have a little voltage draw for to keep the computer live and to keep a car alarm actively set with a flashing led light. If you need further assistance with your battery, then seek out a professional, such as one from Your Mechanic, to help you.

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