why is my car battery going dead from humming under dash on passenger side?

1996 FORD PROBE
150,000 MILES
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I am trying to figure out why my car hums when i hook a battery charger up to it even when the ignition is completely off. I can charge the battery fine. The alternator is good because i can disconnect the battery when started, but when i let it set it goes dead really fast. The humming is coming from the passenger side in between the dash and under the hood. so i cant get to it. The idle sensor is also bad and was wondering if that might be causing it? any help would be appreciated. thank you.

ps. i hooked up to diagnostics and no codes came up?
Feb 27, 2012 at 10:55 PM
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CARADIODOC
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DO NOT DISCONNECT THE BATTERY WHILE THE ENGINE IS RUNNING!!!!

That is a sure-fire way to destroy all of the computers on the car, especially if you raise engine speed at the same time. I used to do that every year to show my students the damage that can be done.

If you want to test the system, use an inexpensive digital voltmeter to measure battery voltage while the engine is running. It must be between 13.75 and 14.75 volts.

Test the battery too by measuring the voltage with the engine off. Holler back with those readings.
Feb 27, 2012 at 11:09 PM