On the standard steering wheel the tip buttons are just wired in parallel with the switches in the shifter. On the MFSW they are wired in to the module in the steering wheel which then talks to the module in the relay box, which then sends on the relevant commands to the radio or TCU, I think via canbus although not 100% on that. It might be wired in to the shifter - I'd need to check the diagrams.
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