Auto Repair: The Battery

Man replacing a car battery.

The battery is the big box that sits under the hood, usually up near the front of the vehicle. It's filled with acid, distilled water, and a set of plates that are combined into "cells" (see Figure 5-3) that produce electric current for starting the car, turning on the lights, and powering the ignition system. The battery also stabilizes the voltage in the electrical system and provides current whenever the electrical demands exceed the output of the charging system.Quite a helpful gadget!

On the battery, attached to either the top or the sides of the box are two large metal terminals. One is a positive terminal; the other is a negative terminal. You can tell which is which because the positive terminal is usually larger and may have a "+," "POS," or the word "Positive" on or near it. Thenegative terminal usually has "–" or "NEG" on it.

Tip: On many vehicles, there's a red cap on the positive terminal, and the battery cable leading to it may be red as well. The cable to the negative terminal is usually black. The clamps on the cables that you use to jump-start a dead battery are usually colored red and black so that you can easily match them to the terminals.

Most vehicles are negative ground, which means that the wire from the negative terminal is attached to the frame of the vehicle to ground it; the wire from the positive terminal leads to the starter, ignition, and so on.

Today, most batteries are sealed and don't require much maintenance. However, deposits do form on the terminals, and they can impede the flow of current.

I know what the problem is; I just don't know where it is...

After I took my first class on the electrical system, I went out one morning and found that my car, Tweety Bird, wouldn't start. I remembered my instructor saying that if you hear a clicking noise (that's your solenoid) but your engine won't start running, you probably have a loose wire somewhere between the ignition switch and the starter. So I opened the hood (it was only the second time I'd gotten that far) and peeked in. Sure enough, I saw a cluster of wires on the firewall in front of my steering wheel. I could see where the wires ran along the frame of the car to the battery, but after that I got lost. I ended up calling the AAA.

When the AAA truck arrived, I proudly informed the technician that I knew what was wrong. "It's just a loose wire between my battery and my starter," I announced. "Then why didn't you fix it yourself?" he asked. "Because I don't know which gadget is the starter!" He was nice enough to keep from laughing, and I felt better when the problem did turn out to be a loose wire on the starter. He also pointed out the starter and showed me the wires that connected to it.

Figure 5-3: Cutaway view of a battery.

From Auto Repair for Dummies, copyright © 2009 by Wiley Publishing, Inc., Indianapolis, Indiana. Used by arrangement with John Wiley & Sons, Inc.

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