Thanks, if that diagram is electrically "legal", then what I want to do should work. I wonder if one of those circuit isolators made for car stereo systems would work for the fish finder interference. I will fuse everything, I made a couple panels for the connections at the bow and already installed panel-mount fuse holders next to their respective 12v sockets.
Next question along the same lines, I have a 2 bank charger to hook up to the 2 trolling batteries, do you guys disconnect the common wire (24v) between the batteries before you charge or can I leave it all wired together and just plug in the charger? The charger will be hard-wired to the batteries.
-brian