He just spliced into the brake light wires, you can see the splices in your picture. You will probably have the dash light up when you plug in. Not sure exactly though, the relay coils may draw so little voltage that it won't trigger the LCM light alarms.

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2003 3.0 5MT Topasblau
Purchased in 2016 and sold in 2024
2012 35d Platingrau