rx7duck

I just got a Nokia handsfree kit (CARK-91) and am about to install it in my '89 convertible which has a factory radio mute button. Anyone know how I might hook up the handsfree mute wire to my RX7's mute button?

Here's the description of the mute wiring from the handsfree kit installation guide:

"The car kit offers a feature that can mute the car radio automatically during a conversation. This feature is convenient and provides for safer handsfree operation. The car radio muting feature is based on a grounded line, so it means that in standby, the yellow wire (XCRM) is not grounded and car radio works normally, but during a call, line is grounded and car radio is muted. "

Thanks in advance for any help...