Re: Pre wired or ???
The stuff under The hood is there. The switch and wiring controls a relay in the box behind the battery so is the way to go.
The connector in the pillar can be used to connect the + wire going up. It will take a small spade connector, female. It is the smaller size like 1/8" often used for speakers. Available at any auto parts joint. I think I got a 50 pack from Amazon for about the same price. I insulated it with heat shrink as the contacts are way close together, a ground is right next to the positive contact or pin. I just used a bolt that was nearby for the ground.