2016 Precedent adding accesories
 

I have a 2016 Precedent with a Subaru Fuel Injected engine. I know there is a rectifier in the accessory harness by the head lights, what is this for? Also if adding extra lighting, USB ports, EcoXGear soundbar, etc. What is the best way to do this? Also get a better battery? I will run everything to their own switches, fuse block/ground block etc. Charging voltage shouldn't get high enough to damage any 12v accesories, just wondering if their is anything to look out for? Or just wire it like I would an electric cart after installing a reducer.