I got Ailiner travel trailer. I don't need to connect up the trailer breaks but I do need extend my current flat four pin trailer connector to a 7-pin to charge the trailers battery. I know I need take an extra connection from a "fused battery lead" but I ask where can I do this from the raed wiring harness. Maybe the red lead that runs with the black lighs lead? or must I wire directly from the LC's battery?