by Matt Larson

Created on: March 04, 2007   Last Updated: April 10, 2007

When it comes to cars, any "do-it-yourselfer" will tell you, that in the wide spectrum of repairs to be made, electrical ones are, by far, the most annoying and irritating ones to diagnose.

It's no mystery to most people how the electrical system in their cars works. There is a battery that provides power, and an alternator that sustains it. These are the most obvious components, and should be addressed first if one cannot maintain current.

Consider the battery: how long has it been since a new one was installed? Often batteries simply lose the ability to maintain a charge and therefore must be renewed. However, it is in your best interest to make certain this is the problem before rushing off to buy a new one. Spend $10 or $15 dollars to first acquire a "multi-meter" to test the voltage of the battery.

With the car off, the reading between the two terminals on the battery should be somewhere between 11 and 13 volts. With the car turned on, the reading should be somewhere between 13 and 16 volts.

Check the voltage immediately after driving the car, and then check it again after leaving the car sitting for 24 to 48 hours. If the voltage drops significantly during this time, there are two possible explanations.

1) The battery is losing its ability to maintain a charge. To test for this, disconnect the battery from the vehicle immediately after driving and check voltage. Retest after 24 to 48 hours. If the voltage has dropped the same amount again while disconnected, consider a new battery.

2) There is an excessive load placed on the battery while the car is off. Car batteries come with a rating called "amp-hours" which indicates how long the battery can sustain a good charge even with a load placed on it. Most batteries come with a rating of 60 or 80 hours per specified amperage amount (which is an amount of current), so with a normal load most batteries will be able to maintain a charge for 60 to 80 hours (or whatever the specified amp hour rating is). Many things can cause excessive loads while the vehicle is off. Accessories such as amplifiers and security systems can sometimes be to blame, but also consider the possibility that there is a fault in the wiring somewhere, in which case it is probably advisable to put a professional to work.

If the voltage reading does not spike (go up) while the engine is running, there is a charging issue.

If this is the case, it's probably worthwhile to have the alternator tested. Many auto-part stores will perform this service for a marginal fee, if not at no cost at all. The alternator is responsible for maintaining voltage while the engine is running, and if it isn't capable of performing this duty, excess strain will be placed on the battery.

It is also important to note that many significantly older vehicles have a separate component that should be inspected called the "Voltage Regulator." This critical piece maintains a constant flow of power from the alternator to the battery, and if it fails it can keep an otherwise healthy alternator from doing its job. It is important to note, however, that almost all post-1990 vehicles have alternators that have incorporated a built-in voltage regulator.

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