Hi, My truck has a secondary battery tray that was empty when I bought it, It looks like it did have one there at one point because there are battery cables ran to the location that have been taped over. From what I had read, this was to power a trailer (there is a power connector at the wheel well in the bed). What other items were typically powered using the secondary battery? I have a few things not working, including the AC. I noted that the secondary battery positive cable is connected to a power distribution block on the firewall, it also has a cable going to the AC relay on that same side of the block and it has me wondering if if this could be why my AC does not blow cold. I have attached a few pictures. Thanks.