check your fuse panel to see if you have a breaker labeled for a second ac. If you do the wire is beside the vent in the other room. If you don't see a electrical box take a screwdriver and remove the trim ring around the vent in the inside. The wire might be in a box beside the vent inside the ceiling. Once you find the wire adding the ac is easy just remove the vent and follow the instructions with the new ac. It mounts using the same hole the the vent was in.
2007 GMC 2500 Duramax Crew Cab LB
2008 5th Wheel Cardinal 36LE