Tekonsha Brake Controller Wiring?

UPDATE: according to the Tekonsha wiring video (see in the pic gallery) it's just connecting that red wire to the brake switch that's a "mystery" - the rest is pretty obvious (power, ground, and the one hooking to the 7pin). What can I tap into to get the break switch signal? Anybody knows if this is just a on/off or pressure sensitive requirement for the trailer break controller?
UPDATE2: I found this Highlander install, and they do tap the brake switch signal into the hot wire in the actual switch underneath the pedal

Anybody got a clue if it's possible to install a Brake Controller on a Prius? For eg Tekonsha Primus or P3. I've heard loosely about it like it's a unicorn but I can't find any information regarding this.

For eg, on a reddit thread that I can't find now somebody was saying this guy towing that monster of a camper had a Tekonsha Primus installed.

 

Adjusting is is the easy part. For the signal, where did you tap in the Cellica. I'm not so sure where to get the signal. The obvious one is the brake light at the rear end, tapping into one of those (I've seen that in a yt vid). But then that's like a on/off and I'm not sure if that would affect something electronically OR if the brake controller needs any pressure input from the pedal.

 

So, based on your gen2 post, you did tap into the brake light at the back?

EDIT: never mind, I found a Highlander install - they go into the literal break switch underneath the pedal. Something I don't quite understand. It seems to me the brake controller is always connected to the battery, thus always being on - wouldn't it draw power from the main battery? or it's so small that it doesn't matter?

If I tap this at the rear in the light, that would be the same signal as the wire at the brake switch? it doesn't matter where I tap that?