I don't know the answer, but what does that have to do with installing a Pioneer radio?
Anyway, backup light wiring is going to be manufacturer-specific. If you post the year and make of the chassis you have a better shot of getting an answer.
That being said, the backup lights on my Chevy-based Allegro have never worked. I'd like them to, but never really investigated. It's pretty far down on the to-do list.
1984 Allegro M-31 (Dead Metal)