the red and black in the harness together are 12V accessory (red) and ground (black). To me the picture looks like it has a yellow wire that isn't in a harness with anything else, but I'd guess it is 12V constant. The red, purple, and black is the dome light. red and purple are your 12V inputs... I think red is the one that is connected to the door trigger... like when the door is opened it triggers the dome light to come on. Then purple is the semi-constant, meaning it is constant for x amount of time. Some cars have a timer where the dome light won't work after say 5 minutes, where as the door trigger only keeps the dome light on when the door is opened. Then black is ground. All of these wires can be found at the factory dome light. Red could be the constant and purple could be the trigger, I'm not positive. The other thing you have is a wired FM modulator which will connect to the back of the radio.
