Battery grounds.....all other grounds should go to the Neg. battery post. Battery ground should be made to the engine block not the hull....The engine is isolated from the hull by rubber bushings inside the steering pivot point. Grounding to the hull will eventually destroy the boat. I got this info from my boat mechanic and verified it with the folks at Minn Kota. Minn Kota even said that my onboard charger should not be mounted directly to the boat....to mount it on starboard or plywood to isolate it from the boat. I don't think what you have is galvanic corrosion....I think it is being caused by electrolosis from the ground you have to your hull.