The fusebox under the rear left seat. You can see our switch sticking out that allows us to switch the mode of the highbeam switch operation between normal high beam operation and flash-to-pass.

The cover of the fusebox removed.

Here you can see the wiring. It's a bit hard to figure out what is what, because we used some zipties to keep the wiring together. On the right side of the image the 3 wires leading to the switch (2 orange and 1 yellow). The top left yellow wire (flash-to-pass signal) on the connector has a red t-tap on it (bottom left of the picture). This t-tap is connected to the yellow wiring leading to the switch. The green wire just above the red t-tap was cut and the side of the connector was connected via the faston right above the t-tap (this is the normal high beam operation signal) to the switch. The yellow wire via the t-tap and the green wire from the connector side form the 2 options on the switch, while the other side of the green wire serves as the common that can connect to either the green or yellow wire. This other side of the green wire (leading to the front of the car, coming from the body wiring harness, is connected via a faston as well (center of the picture) which is connected to the other orange wire leading to the switch.

Now we can put the fuse box cover back on.

And you have a switch that allows you to switch the highbeam switch operation between quad-beam and normal.