Maybe I try and explain this a bit more! 
Right now I have to chose; do I want to plug in CD Changer, or maybe Intravee, or now maybe RaspPi + PiBus?
There is ONLY one 'Channel' originally CD Changer with 5 wires, 3 on one connector and 2 on the other.
What if you could select different inputs; CD Changer/Intraveee/RaspPi+ using a 'Select switch' on the steering column.
The select switch could be E53 X5 Intensive Wash button...
https://goo.gl/images/MHwvG7
Plug 3 devices into a selector and use a relay to activate select button?
https://goo.gl/images/PnKjRj
Right now I have to chose; do I want to plug in CD Changer, or maybe Intravee, or now maybe RaspPi + PiBus?
There is ONLY one 'Channel' originally CD Changer with 5 wires, 3 on one connector and 2 on the other.
What if you could select different inputs; CD Changer/Intraveee/RaspPi+ using a 'Select switch' on the steering column.
The select switch could be E53 X5 Intensive Wash button...
https://goo.gl/images/MHwvG7
Plug 3 devices into a selector and use a relay to activate select button?
https://goo.gl/images/PnKjRj