ScottyT- no, it does not go to the charger. I put the new Iota charger in this spring. It goes connected to the AC panel, and then directly to one of the batteries in bank 2.
The wire may even have been an old bilge pump, for example, that is no longer there / in use. Who knows. Whereever it goes, it is getting DC voltage, that is not wired through the panel, and it looks like original wiring.
Patrick - thanks for the advice on the wiring chart. I will calculate things before replacing. I still may ot go with the "proper" size though, as I will not be having all of my DC lights, water, bilge, pumps, etc on at once, and even a jump from 14 Ga to 10 Ga would be a huge improvement. Getting a larger wire over there may be very difficult!