I have read your first post. Sorry perhaps I’m not fully understanding what you are saying. If I understand correctly, you’ve removed ALL aftermarket devices and returned wiring to factory spec yet the aftermarket battery shunt fob still functions on the car? If that’s the case then something’s missing here or rather something’s still present on the car that doesn’t belong. Perhaps there’s an additional device connected to the immobilizer. I still think either there’s a ground issue or a voltage issue. Have you checked all fuse blocks and junction boxes as well? Have you used a proper VOM to watch voltage on the car itself? It needs to be above 12.6v resting over time, if it’s less than that even after 24 hours, it’s a battery fault or parasitic drain. With the alternator running it should be a constant 14.3 volts +/-