Alpine Audio Interrupt feature

Hello.  I've recently purchased an Alpine CDA-9830 in-dash CD Receiver.  The Pink/Black wire in the harness is for "Audio Interrupt".  It appears that certain accessories (i.e. cell phones) can mute the CDA-9830 by sending a "signal" to the pink/black wire. 

Can somebody please tell me what this "signal" is?  Is the Audio Interrupt feature activated by grounding the pink/black wire or by applying a voltage to it?   If a voltage needs to be applied to the pink/black wire to activate the "Audio Interrupt" feature, then what voltage is it? (13.8VDC?)

I don't have an accessory with a wire lead to go to the Alpine's pink/black wire, but I have another project in mind that could use the audio interrupt feature on the CDA-9830, which is why I need to understand whether it is a ground or voltage application to the pink/black wire that activates the audio interrupt.

Thanks in advance for any replies!

Thanks, mobile1.  I'll give that a try. 

After I posted this message I was able to locate an owners manual for the Alpine CDA-9820.  In that manual they indicated it was "ground to activate".  It appears that Alpine left this information out of subsequent manuals.

Thanks again,

-Dan