[Silverwanabe]

I have cut the hole in the ceiling for the new AC.
(I have not trimmed it exactly 14 x14 yet)

There are two wires located in this area.
Which one do I use??
Why 2 wires?
Both are Kaiser Aluminum .
One has a bigger diameter and there is one like it in the trunk area not connected the the breaker box.

Also, there are two ribs running parallel to the new hole in the ceiling, a few inches from each side, running fore and aft.

I am assuming this is where the AC support frame ties into the structure for support.

Suggestions are welcomed.

Enclosed are 4 pics.