using multimeter you can test it.. the pin inside the connector is shorted to the pins outside the connector... and the internal body is connected to other pin visible outside..
the third pin is shorted to either the pin or the internal circular surface.. the pin is positive and the internal body is ground.. so when you mount the pins shorted to the pin inside the connector will go to ground and the pin shorted to the internal surface will be connected to greound... the third pin is obviously shorted to on of these pins if not short it using wire on the board...
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