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I installed a new battery 2 days ago and now it is completely drained. Any idea where to start looking for the cause? All lights were off and I have no radio in her. I have a bat cutoff switch but I forgot to cut it off.
 

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Start looking at all the main power feeds and see what's hot when the key is off.
 

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Does the alternator feel hot?
 
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Back during my build my donor alternator drained current all the time leading to a frequent flat battery. I got a tip on this site like "egchewy" above and replaced the alternator. End of problem. First time in my life I had ever encountered such a problem. Unhook you alternator feeds and see if the problem disappears.
 

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A friend's charging system wasn't charging. He always kept the car in a trickle charger and could drive for short periods but after a while It would run out of juice. Replacing or fixing the alternator circuits took care of it.
Jim
 

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What Chewy and Warsaw Jim said. If you have a bad diode in the alternator it will load and drain the battery. If this is the case the alternator case will often feel warm.

Jeff
 

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A cheap easy check for battery drain: Place a test light between the negative cable and terminal. If the light glows you have a drain (something on) . Start pulling fuses to see what circuit it might be.
 
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No problem. Car and any power stuff off. Remove the negative cable and put test light on battery terminal and the test light clip on the negative cable. If it glows, something is pulling electricity.
 
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Right you are. First move would be to disconnect alternator...get that possibility out of the way....then pull fuses. Years ago when I had my repair shop, any car that came in with a dead battery, the first thing I would do is hook up a charge box to see what came on...usually a headlight switch in the on position....or a dome light...this is in a past lifetime prior to intelligent body control modules ...or cars that switched lights off automatically after shut-off. Since then I stopped telling people, "hey, you left your lights on!" They go off by themselves was the usual (embarrassing to me) reply. Live and learn!
 

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Get your hands on an ammeter. You're measuring CURRENT, not VOLTAGE. Begin with a HIGH scale and choose lesser scales until you have a center-of-scale reading (unless you're using a digital meter). Begin DISCONNECTING things (one at a time, preferably) until you see the load drop... that'll be your culprit. You can most likely accomplish a LOT by pulling fuses, one at a time... Oh, and a current meter goes in SERIES with the battery lead... be sure to start out on a HIGH CURRENT scale so you don't zorch the meter movement.
 

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If your car is computer controlled and fuel injected you're always going to have a draw for the keep alive memory so the test light trick will fool you. A low amp probe around a battery cable with the circuit complete would be ideal, an inline ammeter would be my second choice, and if neither were available I would use a voltmeter inline. Keep alive memory is usually 9V. If you have battery voltage through the meter you have a draw. Remove fuses until the draw goes away and then look at devices on that circuit.
 

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You didn't mention what alternator you are using. If it's the Fox Mustang-style alternator, one thing that will cause this, is the case of the alternator itself. Run a #10 wire from the back of the alternator to frame ground. Can't say why this frequently works, but it does. It's been a while, but I believe there is a threaded hole on the back that you can attach a bolt and cable to.
 
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