Either one or other is connected.
Radio uses 5v logic as arduino.
Difference is 100mV max.
I`m using MCP2025 transciever chip to convert ibus to ttl 5v, but I need to disconnect it from radio, not arduino, so I need to disconnect 12v side....
About BMW... yes. I would get e60, but I rather took e39 because of the problems of newer BMWs.
Radio is actualy made by Becker.