I did a fair bit of work on how to have an I2C link over a few meters. The best and current way I found to do it reliably is with an I2C bus extender. The one I used is the P82B96. You need one on the AOG PCB in the cab and another one in the waterproof box on the roof. I posted a schematic and pictures of the setup a few days ago :
You can use 5V instead of 12V on the bus. The level shifting is also done by the driver, so you can have 5V on one side and 3.3V on the other. Also, I only had unshielded cable at my disposal, but if you can, use a shielded cable grounded at one end to get a better immunity against noise.
With that, you can run I2C anywhere you want on the tractor !
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