I had a really bad interference problem on my Garmin Striker Plus 4cv whenever I used my Minn Kota Endure C30 trolling motor. I have a PWM setup and it caused horrible interference.
This may not work for everyone but it fixed 100% of my interference problems. I simply put a stainless steel hose clamp around my motor and ran a ground wire from the negative on my trolling motor battery to the clamp. I didn't sand the paint off my motor or drill into it to make good contact. I simply pinned the wire under the clamp as you can see in the photo below.
I cannot explain how/why this works but I guess the clamp itself acts as a ground into the water?
Anyways, it's cheap to try and i hope this helps someone else. It's so nice to finally be able to use my fish finder with a nice clean image: š
Posted by MooseLipps