When the harness is released is June alongside the write up, I will go into more in depth explanation. These are all connectors and terminals from one of Toyota's OEM harness and connector manufacturers. To answer your question, this harness plugs into your door so that you can plug the premium mirror in without having to cut or splice wiring due to the different connections and wiring. You don't have to do anything inside the mirror for the turn and puddle lights. This will also allow you to be able to still run your original mirrors should you ever need to. Just simply unplug the harness from the original door connector. PM me if you have any more questions.
I stumbled on this when looking on if it is possible to swap mirrors for the Pro to gain the TS/PL. Old Red will you been releasing these for purchase soon?