wiring the power postive and negative connection to fuse box

Hi Everyone,

I was wondering if any one know where the fuse box is. i think underneath the left vent.
I need to install a mirror monitor for my back up camera. There is 3 rca cables.
The yellow one i assume is for the male yellow rca from the camera, the white one i dont know ,does that need to be plugged in , the third is a red rca with positive and negative.
The instructions saids i need to connect the positive wire to a 12+ constant and i assume the black negative wire will connect on the chasis of the car for ground.
Now i was thinking of using a fuse tap, maybe look for a open spare fuse to see if that only turns on when the car is on ,i dont want to drain the battery.
I just want the monitor to come on when in reverse and off when i am not in reverse.
The third thing is if i wire tap this what fuse amp should i use , i was thinking at least 15 because the cigerette uses 15 amp i think.
Any suggestions would be fantastic.