I use one of these connectors to connect my winch
control in the aft cockpit
to the removable remote
control cable and switch. There are three points of connection which make it ideal for this. These connectors have been used for a lot of different applications. If as you say, the wires are all connected to the dc negative ground bus. a few possible options could be considered. 1. A point to attach an overboard
sacrificial zinc. 2. Old unused telephone connector with wires tied to ground for safety
. 3. Any number of ideas the previous owner may have had.