The windshield I am installing here is a Givi D323DT, which is the largest windshield they make for the PCX. For the D323DT in particular, Givi recommends you use mirror extensions, which Givi sells specifically to accompany the windshield. The part number is D323KIT for the extensions. The mirror extensions include instructions and are easy to install, so I didn't bother with pictures of that process. I have since removed the extensions -- if you adjust your handlebars and mirrors, they are entirely unnecessary.
Here's the windshield in box next to the scooter:

Still wrapped, leaning on scooter:

Start the process at the front of the bike, under the center fairing:

If you look up under there, you can see some screws:

Take the screws out:


Stash the screws somewhere and then GENTLY pry off the top of the white panel you just took the screws out of:

Then do the other side:


Gently pull the panel down and off the bike:



Grab your 10mm ratchet:

And remove the four bolts securing the windshield, two per side:


Gently pull the windshield off one side, then the other:


Nekkid PCX:

Unwrap your shiny new windshield and place it over the four studs that held the old windshield on:


Wrench it back on. Remember, the plastic washer goes between the bolt and the windshield! It should go PCX interior | Windshield | plastic / rubber washer | nut. Tighten until it is tight, but DO NOT OVERTIGHTEN! You could crack the windshield:

Slip the plastic fairing back in place:

And screw it back in place. This part sucks (it is hard to get the screws in place), but if you have a magnetic screwdriver, it helps a lot. Do not put the top of the fairings in place yet, otherwise you won't be able to get the fairing on right:

Click the fairings in place at the top once the screws are in place. They should click when they go in all the way:

And the other side:

You're done!
Enjoy the results:
