That light brown wire with the white stripe remains a single into the bulkhead, doesn't it? I think without rally gauges there's two wires at that bulkhead connector.
Anyway, I've been thinking about your problem. What I would do is try to pass a wire through an empty slot in the bulkhead connector. There should be room. Once I got a wire through, I would crimp an eyelet to the engine side and connect that in place of the current brown wire. Then I would pull the orange wire out of the connector and solder the other end of that alternator wire to it. That way, you're bypassing all the burned stuff.
Tape the new wire along with the wire harness that already goes to the bulkhead connector from the engine side. And tape the new wire to the orange wire on the interior side.
