This HB has the C Charger 9000 series, boat is 2005. When installing a new batt, without the Charger plug in I get an arc.

Nothing else on terminal except the 2 leads coming from the Charger unplugged.

The water pumps and a couple other items are on a independent battery as well so I know they are not an issue.

Assuming 12 volt house lights or the Charger is my issue.
Your thoughts of where an how to track down the short