I suspect the 30 amp blade fuse is the solar connection. Do you have a solar controller? If so, disconnect the solar panel input to the controller (or cover the panels), then pull the 30 amp fuse. Does your power tongue jack still work? If so, that fuse is the solar input to charge the batteries. Solar panel input to a controller not connected to a battery can damage the controller so I would not just pull the fuse to see what happens.
With the solar input safely disconnected, you can remove the other positive connections and test which one still has 12vdc coming from the converter. That will also be connected to your 12vdc main line. Be careful, do not allow it to be shorted to ground.
As another suggested, you should mark your cables where they all go. Mark the positive ends with red electrical tape or shrink wrap and the negative ends with black tape or shrink wrap IF they are not the correct color to start with. This will simplify future electrical issues.
