I don't see any reason why you could not use your generator wires that run to your 12 volt battery. I use 2 12 volt batteries. One is located in the existing battery location on my TC. The other I put in my former generator compartment. My solar goes to the controller, then the generator compartment into the first battery. From there I use the existing 4 gauge wire that runs to the battery compartment. Works just fine. In a perfect world I would have my two 12 volt batteries in the same location but with the heavy gauge wire between them and the small loads I am not too concerned. The two heaver gauge wires I assume are running to your house batteries for starting you generator. That is/was how mine was wired. Those are the wires I used to run to my existing battery. You will need to make sure that is how yours is wired. The solid wire romex type wire is what supplied 120 to your transfer switch. I am no electrician so make sure you can verify before doing any damage to yourself or your rig. :) Also you need to make sure those romex wires are not hot when plugged to shore power. If so they need to be capped off. But you could actually take the transfer switch out if you are not going use it anymore. JMHO
