View Single Post
Old 06-26-2008, 04:14 AM   #8
Registered User
Join Date: Jul 2007
Location: Santa Barbara, CA
Posts: 10
My Ride: 2003 330i ZHP
Originally Posted by ccfj1 View Post
Indeed, If you have a DVM then attach one of the probes to the "tel-on" wire and see what happens, I shouldn't think it will do any harm, ie pulling the wire to ground, like you say worth a try.
We were close!

I managed to find one thread on another board that came up on the 5th page of results from a google search - the TEL ON lead needs to see +12V to enable the telephone audio inputs on the head unit.

I of course don't have a 12V lead that is switched at the same time as the Parrot mute lead, but it turns out, the BMW head unit doesn't really mind if you leave the TEL ON switched high all the time! If I turn the stereo volume down really low, I can tell there's some hiss injected from the Parrot unit, so I'll probably put together a quick relay to switch 12V to that input when the Mute lead pulls to ground, but for the moment I've got a system that will work.

I figured I should drop in and mention this because there appears to be no more than one or two individuals in the history of the internet who have actually explained how this works. Hope this does someone some good who is up against the same issue and for one reason or another does not want to use a commercially sold harness.


TEL MUTE = Pull to ground
TEL ON = Pull to +12V

If you do BOTH of these things, you will mute all audio sources and enable the telephone input. If you just MUTE, you kill audio sources but get no telephone. If you just activate TEL ON, I suppose you could theoretically just mix your telephone audio into your music, but I can't imagine that being particularly useful for most people. Maybe if you REALLY wanted to let a friend listen to the song that's playing on the radio at that moment. There's an idea. Put a hidden switch on the Mute lead. Just in case.
zerodb is offline   Reply With Quote