Lesson 3/Learning Event 3
The jacks for various tests are usually located around the edges of the meter. There may be a
common jack. This is used for the negative lead for all tests. The positive lead is placed in the
appropriate jack for the test being made. In some multimeters a range selector switch is used
instead of separate jacks for each range, and these meters have common positive and negative
jacks.
The rheostat knob is used to zero-adjust the meter for resistance tests.
The switch knob is used to position components of the meter in the proper circuit for the test to be
made.
The meter dial usually has three scales:
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One scale is for DC measurements. It can be used for either voltage or current.
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Another scale is the ohms scale. Remember, the scale is read from right to left. In other
words, if there is no resistance in a circuit, the pointer will go all the way to the right or to
0 ohms. As resistance increases, the pointer will stay farther to the left.
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Another scale is for AC voltages.
You must remember that all meter scales will not be the same. You must use each meter in
accordance with the way it is designed.
As you gain experience in automotive electrical system repair, you will learn the approximate
resistance of each component. For example, you will learn that if the circuit is connected with light
wires (18 gage or smaller) the current flow is going to be low. By dividing the approximate current
flow (amperes) into the voltage, you will get some idea what the resistance should be. Always
check the specifications for a system or component to get the exact amount. You should be able to
find either the current or resistance for most components in the technical manual.
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