how can you check polarity of a cable with a multimeter?
check for resistance in the wire and connector. Hold one probe on the sleeve of the connector (I assume you are talking about DC plugs) and then touch the other probe to the ends of the cables. The one that registers resistance is your ground or (-) wire.
So the outside of the plug should be connected to the white cable, which in turn should be connected to the -V of the powersupply
so normally putting one probe on the outside (sleeve of the connector) and the other at the end of the white cable gives me a reading on resistance
putting one probe on the inside of the connector and the other at the end of the white cable gives no reading
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