I'm working on a project where an Arduino MCU is listening to a vehicle CAN bus. Because of the location of where I need to tap into the bus, the MCU needs to be inside the vehicle cabin. But also, the MCU needs to drive some automotive relays that need to live in the engine bay.
I'm designing a solution with some small optocouplers that drive the automotive relays. The question I have is can I drive another board in the engine bay using straight GPIO connections over wires of that length, or do I need to look at something like LIN or CAN to talk to another MCU in the engine bay on the relay board? I would expect the wire length would be around 4' long, and obviously a noisy environment.