OHM'S LAW:

 Ohm's law, a basic electrical rule, states that one volt (of pressure) is required to push one ampere (of current) through one ohm (of resistance).

This fundamental rule is applicable to all electrical systems and is of outstanding importance in understanding electrical circuits. It is used in circuits and parts of circuits to find the unknown quantity voltage, current or resistance when the other two quantities are known.

Using Ohm's law, the unknown quantity is determined as follows:

To find the amperes---divide the voltage by the resistance.

To find the voltage---multiply the amperes by the resistance.

To find the resistance---divide the voltage by the amperage.

Remember this --the current that flows in an electrical circuit is the balance between the applied voltage and the total circuit resistance.

It will not be necessary for you to stop and compute electrical values, using Ohm's law, during a tune-up. It is advisable, however, that you have a basic understanding of its application. Your test equipment works out these problems for you, giving you the answers in the form of meter indications. With the assistance of the equipment, your attention is quickly directed to the source of the trouble.

As a general automotive electrical system trouble shooting rule, remember this--if the voltage remains constant, as it usually does except in the case of a discharged battery, an increase or decrease in current flow can only be caused by a change in resistance.