I have few suggestions that you can try. How much power are you trying to get through the systems. If it a low power, you can use double pall double throw relay and use the coil connected to power from wire 2. When the power is off on line 2, line wire connected 1 is always connected.
See the diagram below
It's only going to be 12v dc power so not too much. I do also need it to be weatherproof as it will be exposed to the elements at almost all times.
If that is the case, you will need a 12 Volts DPDT relay.
See the link below
One of these would work. You will need to wire it and based on the diagram on the side of the relay.
When it come to waterproofing the system, I would suggest purchasing a weather proof epoxy that can be used to cover the terminal after all the connections have been made and the system has been tested. This way you have room to make changes and get to test your circuit. After everything is working, then you will mix the epoxy and apply it on the terminals and cover the relays.
Here is link for the material