Nokia handsfree mute wire

Am after some help with this one, seems to be quite topical on most forums, but there is never a definitive answer.

I have a 1998 P11 with a factory fitted Blaupunkt, the one that has a cd changer option. The handsfreekit works perfectly, managed to work those wires out, but in the drivers manual, it says that there is a mute option. Can I find the right wire, or a wiring diagram. No.

Please, if anyone has an idea, post it. It's driving me nuts.