Ralph, I share your concern about a parking mode failure causing a depleted battery. I think the easiest solution, and also failsafe, is to use a mechanical SPDT switch wired as follows:
- Hardwire the Red wire so it is always connected to an Accessory fuse that switches on/off with the ignition.
- Wire the Yellow wire so that the SPDT switch connects it to an always ON fuse (battery) in #1 position, and to the Accessory fuse (with the Red wire) in #2 position.
Switch position #1 enables Parking Mode (Red -> Acc, Yellow -> Battery).
Switch position #2 disables Parking Mode(Red -> Acc, Yellow -> Acc). The camera only powers up when the key is ON, and power is completely removed from the camera when the key is OFF.