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How to Use an Ohmmeter on a Car

    • 1). "Zero adjust" the meter. With your left hand, firmly hold the two leads of the meter together. With your right hand, turn the small knob until the needle points to zero (or the display reads 0.0 for digital readouts). This must be done before every reading. Left handed people should switch hands for the process.

    • 2). Find the component you want to measure. If the meter reads zero, there is a direct connection (a "short") through the object being measured. If the meter reads "infinity," there is no electrical connection (an "open") through the object being measured. In a car, measuring across the points should read infinity when the points are not making contact, and zero when the points are making contact. Any other reading means that the points need to be replaced.

    • 3). Reverse the leads and measure again. Some objects obstruct the flow of electrons in one direction, but not in the opposite direction. Such objects must be inserted in the correct direction to work properly. This is true for the diodes that are used to electrically isolate different car components.

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