I have searched the forum, but most vaguely relevant threads are years out of date.
My car is a Lexus RX400h 2008, Mark Levinson sound system.
I bought a generic Bluetooth, usb, 3.5, adaptor. I also bought a Y splitter. I installed everything and the Bluetooth worked just fine. Didn't actually try usb etc.
Then I connected the existing connection, which I now know includes air con at least. The outcome is that I cannot connect both. One or other work if connected alone, but connect both and the Bluetooth doesn't work.
My previous research suggested it was just the CD changer that would be affected, something I could live without, but air conditioning is another thing. The screen goes blank and tells me the 'system' is not connected.