You don't need power applied to measure resistance.
If you pull a fuse you can measure resistance on the downstream side of the fuse to ground. It should be a high reading.
A 10a draw will be on the order of 12/10=1.2 Ω.
https://www.realoem.com/bmw/enUS/sho...diagId=61_1308
Good news the 4.4 has the same B+ terminal as the 3.0.
Remove the terminal post in the engine bay on the firewall and that will disconnect the main unfused cable.
Disconnect your battery when you aren't using the car or keep on as charger. 10a will ruin a new battery pretty quickly.