CatFan,

Thanks for the quick reply with some great information.

All of my electronics cabling (power wires and transducer cables) run down the starboard side of my boat to a dedicated battery. I have a separate battery for engine start, lights and pumps. All of the trolling motor battery cables run down the port side of the boat. I do not have a jumper wire between the engine battery and the trolling motor batteries, but when tested with an ohm meter it appears this circuitry is wired into the boat. I will retest it and add a jumper to test effect.

Should the separate electronics battery be jumped as well?

Recently I replaced a bent shaft on the trolling motor and played with the interference relative to the transducer positioning. It really worsens when you approach the head of the trolling motor with the transducer. The cables up the shaft did not have a lot of influence.