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My friend has a newish (~2009) Toyota Tacoma that apparently can short the battery when he turns the key from off to start too fast.

By short I mean, when fully charged the truck will click once like it's dead and then need a boost. I think this has lead to the quick deaths of multiple batteries.

Any other info needed? If not, does anyone have any ideas?

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I think some more information might be useful. What's the exact sequence of actions? How much time passes? Call me a skeptic, but I would think that a battery "shorting" to "dead" that quickly is likely to be pretty dramatic, and I don't see how a fast key turn could result in shunting that much current. I think there's a good chance that something else is going on. –  mac Dec 12 '12 at 4:00
    
also, an edit to the question might be in order to highlight your question...I think your question is "what is likely to be causing this behavior?" –  mac Dec 12 '12 at 4:02

2 Answers 2

Its not a short, it's a bad connection. Typically at the battery terminal, but maybe the main body ground off the battery or main connection at the fuse box off power side. Seen it a lot as a tech. Check for looseness or corrosion.

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Sounds most probable. I'll give it a go when the truck is back in town. –  Eric Fossum Dec 18 '12 at 18:08

You answered your own question. You've got a short. Until you find and fix the short you're going to keep ruining batteries.

Edit: Turning the key in any fashion allows the current from the battery to travel throughout the car ( turning the key connects the circuit ) and reach the short that's killing batteries. If the speed at which you turn the key really does make a difference, then it's possible the short is located in the ignition switch itself. But like mac, I too am skeptical that turning the key fast or slow is significant, without more detail.

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But, that doesn't explain why it shorts only when the key is turned fast. –  Eric Fossum Dec 12 '12 at 21:21

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