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Q: Car dying after sitting for a day. Running out of ideas as to why.

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I have an 04 Mustang convertible. Was running fine 2 years ago when I got it. At the end of this last summer (about 4 months ago), it started dying on its own. I'll let it sit for a day or two while I'm at school and when I come back, the battery is drained. Replaced the battery twice and alternator, but no help. Taken to a ford garage and they just replaced the battery and said it was fine. Checked for any lights that might stay on when the car is off but found nothing. Running out of ideas. Any help would be much appreciated. Thank you.

My car has 124000 miles.
My car has an automatic transmission.

If you have a new battery and the charging system is working properly, and yet the battery is discharging enough that when the car is off you cannot later re-start it, there is only one possible cause. There is an electrical load on the battery that is not supposed to be there, possibly during the normal operation of the vehicle and when the vehicle is turned off, too. The solution is to to insert an ammeter in series with the battery and the car’s electrical system. If there is a load that is not supposed to be there, when the car is off, the ammeter will read a value in excess of about 50 milliamps (approximately). If there is an excess electrical load, the certified mechanic will test each branch circuit account until he finds the one(s) that are supplying the "parasitic" load. It is painstaking work but basically you have to simply test each and every individual circuits to find out where the fault is, that is find the wire or device that is consuming power when the circuit is supposed to be "off" or dormant. The fault could be found on the first circuit...it could be found on the last. If you request an electrical diagnostic though, the responding certified mechanic will certainly find the fault and estimate the cost to repair it.

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