car battery replacment

i just tried to replace the battery in my 87 honda accord. i hooked up the positive cable - no problem. however when i went to hook up the negative cable the car emitted a loud, hellishly piercing noise. just for kicks i reversed the order and hooked up the negative cable first and when i tried hooking up the positive cable the same noise was made.
does anyone have any idea what is happening - what i am doing wrong?


Don’t suppose you could put a wav file in so we could hear the noise? My first guess is there is a short in your ignition switch (may explain why you’re replacing the battery) and it’s sending current to the solenoid and/or the starter motor. Try disconnecting the solenoid and/or the starter motor and then reconnect the battery to see if the noise is still there. Other than the horn, there’s not a lot of things that I’m aware of that will make such a noise without the engine going.

Where exactly was the noise coming from? The battery? The horn? The radio speakers?

Somebody please correct me if I’m wrong on this, but I was under the impression that hooking up the negative (ground) terminal first was really, really dangerous.

When the negative terminal is hooked up, the entire car (pretty much) is at the battery’s “ground” potential. If you touch the positive terminal (such as to hook up the positive cable) while you’re leaning against, say, the fender, you’ll complete the circuit with your body. It’s just like putting a hand directly on each terminal.

Are my fears here baseless?

Possibly. I mean, it’s only 12 volts after all. While you can be shocked from it, I have touched the terminals many times with bare hands and never received a shock. Still, under ideal circumstances, you could get a nasty jolt.

The frame of most automobiles is negative. You hook up the negative terminal last, because when tightening the postive terminal with a wrench, any contact with the frame will spark. The battery can be full of hydrogen gas, and explode with the spark. Attaching the negative last, You only have to be careful not to touch the positive terminal with the wrench. Always jump a car by attaching the positive and negative to the running vehicle’s battery first. The next conection should be to the positive terminal on the drained battery. The last conection goes to a good ground on the dead car, not near the battery. The alternator can be a great ground. After starting the dead car take all the cables off in the exact reverse order. Now that the battery is charging, it’s giving off a lot of hydrogen gas.

I have seen a battery after the starter cable shorted. It took about 15 seconds to kill the power comepletly. The batery was dead the insolation on the starter cable fried off, actualy running down the cable. The battery warped and steaming.

OK, thanks. I’ve always been rather skittish about electrical shocks, and may let that Big Bad Battery appear just a bit too evil in my eyes. :slight_smile:

As Phobia points out, the possibility of a hydrogen explosion from the spark may very well be more of a concern than the jolt itself. I’ve been counseled long and hard about this (after my uncle had one blow up in his face :eek: ), and I always stand waaay back when some fool insists that I don’t know what I’m talking about and jumps his car by hooking the cables to all four terminals. Sigh…

Theoretically, it doesn’t matter what order you hook the battery up (positive then negative, or negative then positive). But there is a practical safety reason why you should hook positive first on cars with negative ground: when connecting battery cables, you always run the risk of accidentally hitting the (metallic) wrench against the car’s body while you’re tightening the bolt.

Consider both cases:

A. If you connect the negative terminal first, and you accidentally short between the negative terminal and the car’s body, nothing will happen. If you then connect the positive terminal, and you accidentally short the wrench to the car’s body, you’ll be seeing fireworks.

B. If you connect the positive terminal first, and you accidentally short between the positive terminal and the car’s body, nothing will happen. If you then connect the negative terminal, and you accidentally short the wrench to the car’s body, nothing will happen.

Obviously, B is safer.

As far as 12 volts goes, Anthracite is correct - it poses no harm in most situations. Go ahead and stick your hands across a battery; you probably won’t feel a thing. However, there are two notable exceptions:

  1. Broken skin. Don’t touch across a car battery’s terminals if you skin is broken in each place where you’re touching (heck, any battery for that matter). Under normal circumstances, your skin resistance, which is usually over 20,000 ohms, is high enough that the current resulting from 12 VDC won’t be enough to hurt you. But broken skin will offer a lower resistance path, resulting in much higher current from 12 VDC. You don’t want more than about 6 mA to flow through you, which means body resistance of less than 2000 ohms could be harmful or even fatal (depending on the current). Broken skin between two places on your body could easily have a resistance of less than 2000 ohms.

  2. Watches. Don’t let a wristwatch w/ metallic band short between as car battery’s positive terminal and negative terminal/chassis! The resulting current could heat the watch’s band until it glows red hot. Ouch!