Having talked with David Goodson, with Shut Up and Fish, and messaging Wayne P on here about interference, there is no magic solution. Every boat is different. You won't know until you hook up the unit and try it. Best solution offered is direct wiring from the cranking battery to the sonar unit. But that's not a sure bet. Next solution is a ferrite ring.
Wiring to the running lights might work but that wire usually comes from a fuse block that goes to the switch for the lights. Nothing is a sure bet.
Another piece of advice is use a trolling motor transducer instead of the transom transducer that comes with the sonar unit.
There's usually tips offered on the mfgrs web site.