2015 harley phone charger

hey everyone, I have a newer 2015 harley davidson breakout fxsb, which I am planning on wiring in a phone charger to the bike. I know the simple way of using a 12v plug directly from the battery, to a usb adapter, then run it into your pocket while riding, but I don't want to do that.

my bike has a tuner which bluetooths to my phone, i can monitor a whole plethora of parameters while riding. I have my phone mounted to my handle bars, so I can safely view and use this, while riding. what I would like to do is wire a charging cable to the handle bars, the routing i plan to follow the existing wiring for the bar mounted gauge and dash, and because my phone is a samsung s8, which supports adaptive fast charge, I plan to hard wire in a 12v adapter to a key on power source.

I have already gotten the adapter, it is a aukey cigarette lighter usb adapter, with qualcomm quick charge 3.0, and puts out between 3.6 and 12v. (3.6-6.5v @ 3amps, 6.5-12v @ 2a, so max 24w)

here are my 2 questions. first, what size wiring do i need for this, my guess is 16gauge, maybe 14? and second, does anyone know where the best place to get 12v key on power is, up near the front of the bike?

I have disassembled the power adapter, will be soldering the wiring onto the PCB, then waterproofing the unit with silicone caulking before installing on my bike.

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