Need Electrical Help! Hard wiring a garmin.

Trying to hard wire my garmin etrex 20. I have an old 12 volt hook up that fits it. I cut the adapter off the end and I want to hook it up to an "add a fuse" but I am left beyond my experience when I found a white wire surrounded by other wires. can't figure out which is the positive and which is the negative.

and once the add a fuse is hooked up which fuse slot would be best to use behind the coin tray.

in the images i unwrapped the wires surrounding the white wire to expose both.

thanks for any help guys!

 

sorry for posting found my own answer. can't use it because i need a converter. found one on Amazon. MODS please delete. sorry for the time.