Motorcycle Repair: changing turn signals, turn signals, running light

Question
QUESTION: I changed the turn signals on my wifes' sportster, and I'm not sure which wires go to what.  On the new tail lights, they have a black wire and a black and white wire.  The existing wires are one black, one blue, and one purple.  How do they match up?

ANSWER: What year bike are you working on?
Mike

---------- FOLLOW-UP ----------

QUESTION: It's a 1999. sportster 883 custom.

Answer
If you are refering to the front turn signals the black is ground, blue is running light and the purple is turn signal. the rear turn signals have only two wires. Purple/brown is hot and black is ground. Your tail light should have 3 wires, black is ground, red/yellow is brake  and blue is running. One the turn signals you want to install, the black is ground and the black/white is feed or hot.
Good luck and happy riding
Mike