Pick up the rear light and the indicator as an analog signal

Hello, I have a Mercedes-Benz Vito 110 CDI (VA), first registration 2023. A warning light beam is installed on the roof. Everything is correct according to § 52 StVZO. In the warning light beam there are also flashers, rear light and brake light integrated. In the beam integrated brake light must not be clamped in Germany, so this remains jammed. I would like to clamp the indicator and the final light. The warning light beam needs it as an analog input signal. o I pick up these signals? Nowadays even the lighting is running via CAN bus and I can imagine that the original control units of the vehicle don’t like it when I connect more consumers in parallel with the existing lights.