Thanks, this is the best diy on the subject. Only thing I would add is this:
I separated all the retro fit wires and feed them individually through the rubber grommet just fine. No straw or other technique needed.
Use the supplied plastic connection boxes supplied as "practice" and familiarize yourself with how they work and where the numbers of the pins are. You won't need them unless you break on of the connection boxes on your car.
Use an eye glass screwdriver to open up the connection box in the overhead unit. Use the supplied connection box to see how it works. You'll see the little tab the unit needs to slide over the top of.
Remember, all you are doing is connecting wires to already existing circuits. That's all.
You do need to use the above pdf diagram to see where you place the new wires since the pdf links in prior diys are dead. Don't need those directions anyway since what's here is all you need.
The wires only fit in the connection boxes one way and will click when they seat.
And, as mention before, forget any other suggestion on how to remove the top unit with screw drivers or kitchen tools. Just take out the visor clip units. Been there done that. Takes 2 minutes. Just get a Torx set if you don't have one already.