How do you wire a 12 volt cigarette lighter plug on a boat?

pretty simple. on the back of the lighter there are 2 connections one is labled positive, the other is labeled negative. Wire the Positive connector to the Positive terminal on your main battery, and the Negative conector to the Negative terminal on your battery. Easy as pie, 99.9% of 12V lighters already have a fuse in them so no need to worry about inline fuses.