Of course it is, it's simple electricity, current is the flow of electrons, therefore you have to measure this in line.
Volt is a difference in the potential, this difference can only be measured in a parallel circuit.
That's the reason why a voltmeter is for save everywhere, since there is almost no current running through it.

Of course you can measure the current alternatively by using a system which measures the magnetic induction of the flow but this is much to expensive for a car.

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RaymondQV
Countach QV Ex-Mimran #GLA12997, Urraco P300 #20530 sold in August 2008, Jalpa #FLA12203 sold in May 2006
www.countach.ch
www.jalpa.ch

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