At all instruments
Seatalk is a 3 wire connection that ties all the Seatalk(Raymarine) instruments and provides both data and power. So it is available at each instrument and on my H320 at least, at the power panel. As the wireless is a radio link, I would think it should go as close to the center of the boat as possible, on my H320 that would be inside the instrument panel above the companionway. About 8 screws, unplug a Seatalk plug, plug that into your wireless, plug the wireless into the old instrument and you have it, I believe.Gary