12v fuse board

I would guess you ought to remove the green wire, or connect it to the rest of the positive bus somehow. The best would be to figure out where its other end is: it ought to just go to the converter area, and probably isn't connected to anything there, but it's certainly possible that somebody could have altered things around in who knows what ways in the past. Working on older RVs (or houses or cars or whatever) can be somewhat akin to an archeological exploration at times.

It would of course be best not to leave a live wire with the other end loose and not connected to anything.