HK4 Hardwire Kit in a Tesla & Parking Mode & Raspberry Pi

When connecting the HK4 to a car, the RED cable goes to some permanent 12V source. The BLACK cable goes to any ground and the YELLOW cable goes to some source that switches on when the car is running. It is called ACC (or sometimes IGN) because it normally activates when the key is turned into the ACC position.

But what if the car does not have such a power source? In a Tesla model 3/Y (and maybe others) there is no fuse box. There is no easy to find power source that only carries 12V when the car is in driving mode. There are ways to get a permanent 12V that actually carries 16V on newer models, but they are not permanent and neither represent driving mode. In fact, they are powered whenever the car is not in deep sleep mode. When the car is charging, or when the car is in one of the A/C modes or when the car is in Sentry Mode, the 16V is always powered. Which is okay, since the need for the Viofo to run nicely matches the need for Sentry Mode to run. So far so good.

But I would like to activate Parking Mode when not driving. For some reason my WM1 “knows” that when the HK4 is connected, it can obey it’s ACC-signal and ignore the GPS and Motion settings. But since I had to connect the yellow and red lines together to the 16V source, the Viofo never enters Parking Mode! Only when I disconnect the yellow line it immediately enters Parking Mode and stays there until I connect it again.

Now I’m thinking of building something around a Rapsberry Pi to drive that ACC input. It can piggyback on another project I’m also contemplating, so this might sound more overengineerd than it is. If I can determine the driving mode from my code in that Pi, I could trigger the ACC line to the HK4 and switch between Parking and Driving mode. But, now I’ve introduced what I know about the HK4, here’s my question:

What do we know about the ACC input? Of course connecting some random 12V to it, will toggle the Parking Mode flag. But what kind of input is it? Can I directly feed one of the IO-lines to it? Probably not. Or is it some high impedance open collector mumble something? Then the 5V from the Pi might trigger it. Is there some datasheet describing it? Anyone else already did some digging I could not find?