Taillight LED Upgrade Problem

Hi All!

I'm new here! But anyway, in my quest to upgrade my recently acquired 2017 Mazda 3 Touring, I purchased off eBay a set of JDM/Axela-style LED taillights. Well, they are partially plug-and-play, although the product description does say that the inner portions of the taillights need to be hardwired into some existing wiring. I have no idea which wire to tap, so if anyone can chime in with some help, it would be greatly appreciated as I am trying to avoid at all costs taking the car with the lights to a shop to have them installed for a bajillion dollars. Here is the link to the item that I purchased -- https://www.ebay.com/itm/311958938443

Thank you!