Connector X6965 is a soldering point where all those voltage supply lines are bundled together. It's located in E-box where DME also lives. That would be a good place to cut and make the wiring for the switch. The wiring can be routed thru E-box vent route thru firewall. Perhaps it would be wise to put a separate smaller like 5A fuse near the switch so if the line happens to ground on the chassis that fuse would be easier to replace than the one on E-box fuse pack.

https://bmwteka.com/wds/en/e53/493a47c7#

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E39 530dA -02 M-Sport Messing metallic
E53 X5 3.0dA -06 Sport Stratus grey
E70 X5 40d -12 M-Sport Space grey