I have been having issues with the cranking battery always needing to be charged no matter how much I have run- reason for updating to a 3 bank.Boat starts and runs without this connected. What does this third wire power? Afraid to just hook it up to the battery just to find out .Found this when I started to replace original 2 bank charger with a 3 bank.
Part 61A-82105-01-003 Wire battery cable. Heavy guage wires black and red attached to cranking battery; 3rd wire is lighter guage red wire. Found this 3rd wire (has battery fitting) from the battery cable loose in the bottom of the boat. Looks as if it has not been connected for a while.