Diagram to fit a cigarette lighter socket in a boat working off a car battery . how do i do it?

I want to put in a cigarette lighter socket in my boat so that i can plug in a garmin gps 12 navigator. that way i can use the boats car battery instead of 4 x aa batteries wich i would continually have to replace(only 24 hrs power). i could have the gps system walking continually as back up. i need a simple diagram on how to fit this cigarette lighter socket or simple instructions. nothing technical or you will lose me.
Answer
Red wire to +terminal black wire to - terminal