Cigarette lighter wiring

Kind of a dumb question, but here goes. I have an aftermarket "power
port" (lighter without the heating plug) that I'm going to put in the
center console. Bentley wiring diagram says power in is purple, and
gound is black (of course). My question is, on the standard lighter,
which contact is the power in (+), the bottom center, or the side?

-=Chris 

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