Because the meter won't be reading the full current present in the circuit. By measuring current in parallel, you are shunting some of the current across your meter, but not all of it. It defeats the purpose of the measurement.
Originally Posted by robertobaggio20
Sure, but why ? Please do help me understand why it is necessary.
When measuring current at low voltages, it is correct to always put the meter in series with the circuit being measured.
In this case, that means either pulling the neg (-) cable from the battery (to measure total current draw) or patching the meter in place of a fuse (to measure the current in a specific circuit).
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