How many batteries on your boat? Do you have separate ones for the trolling motor and the Lowrance? If so, IIRC, they should share a common ground.
A little more information may help. Are you running a 12 volt trolling motor and sharing the circuit with the other electronics?
How many batteries on your boat? Do you have separate ones for the trolling motor and the Lowrance? If so, IIRC, they should share a common ground.