Ok, so if you want it exactly like the video, then buy the module.
Otherwise, wire it up this way and you can have the turn signals do a wig wag style pattern... Left side then right side...
First, find the turn signal wire. I recommend getting it from the wire harness in the kick panels, this way you are not fishing wires into the doors.
When you locate the proper wire, cut it.
You'll need 2 diodes per side.
The easiest way to do this is to get 3 butt connectors and configure them in the fashion below.
Now I left the diodes long to give you an example of how they should go. Make sure that you cut them so that none of it is exposed; there will be 12v going through this...
Think of Diodes as little "one way" signs for current... You see the silver ring around the one end of the diode? Whichever side the ring is on is where the current will get stopped.
So this configuration will stop the current from going back to the vehicle when the Whelen Flasher is activated AND it will prevent 12v from going back to the Whelen Flasher when you use your turn signal.