@hubert275_171399
Sir, let me state up front that I am not mechanically, electrically, or electronically knowledgeable. So please ignore me and accept my apology if my comments are irrelevant.
However…your mention of the power drain toggling on and off sounds remarkably like what killed the battery on my cell phone awhile back. It turned out that a glitch had the phone actively pinging for system and app updates every minute despite being set to check only once a week.
I have no idea what system or onboard computer in a car could possibly be trying to activate anything. And I realize the idea is almost certainly not relevant.
But it is that consistent, repetitive toggle on and off of a parasitic power draw (if I’ve correctly understood your problem) that sounds so familiar to what killed my cell phone battery.