Car stereos BT typically for music are one way, receive only, will not transmit to BT speakers or headphones. Designed to play your music from the phone or answer phone calls but not really designed to connect to BT speakers.
There are however BT transmitter modules that you can add onto most stereos which allow BT speakers to connect. You may need to get creative to make the connection some stereos may not have line level outputs and you might need to adapt the speaker level to line level..
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