[nimonster]

I have a 2015 Mazda 3 without any Homelink mirror, rain-sensing wipers, smart city, etc. I want to add a dashcam to my car but I want to try connecting the wires into the place where these factory sensors would get power from if they were installed. Will this be possible with both always-on power and switched car power? I don't have that black box that people with the factory sensor have.

 

[Tristan-cx5]

I would recommend to use mini fuse adapters in the driver legroom and put cables up the A pillar. I would guess that if you search for "dashcam wiring" you will get results on how to do that, as this was done many times before. Good luck.
Example link to hardwiring a dashcam.