Ahhhh... let me guess. Premium sound? They have a fader under the cluster that makes the speaker wiring different to most. Just remove the fader from the system and it will all become clear... the wiring goes from where the fader used to be to your CD43 outputs.
BTW: If you have premium sound system, you can use the crossover in the 4-channel booster amp that can be retained when substituting it for a proper 4-5 channel amp. I've written this up in the past, as many have... check the archives et al.