They are lines that are pre run for amplifiers (if your car had the infinity system) and a CD changer. If you got the adapter harness for your radio to a 95 mitsu, then you should be golden, as long as it didn't have the aforementioned infinity system. From what I see at your pictures, that smaller white plug went into the back of the deck. But, if you look at that, you'll notice there are no prongs. That means then, I am ASSuming you don't have the infinity system.
Bottom line, don't worry about them. If everything is already working fine with your aftermarket deck, then they didn't mean crap anyway.