I just got a Pioneer F500BT for my car. The unit is designed to interface with a custom Pioneer amp that bypasses the car stereo output to route voice directions and cell phone calls to the factory stereo speakers. The unit has an "amp control" wire that tells the pioneer amp when to mute the stereo and pass audio control over to the GPS.

My factory stereo in my car (Pontiac G8 GT) has a 'telephone mute' wire and an input (+/- mono) for cell phone audio input. These wires are currently connected to onstar audio.

I am almost certain that the mute wire on the radio will mute the audio when it senses a ground signal. I have tested the 'amp control' wire coming from the GPS, and it is normally open (no positive voltage or connection to ground). When the GPS gives a voice command, the wire then closes to ground, with about a 300-400ohm resistance, and I can also measure about 0.18 volts on the line. So in theory if I can get the voltage right, it will function like a mute wire, muting the radio only when there is audio output from the GPS

First I would like to know if this wire, as it is, will work to mute my factory radio?

Also, if not, I would like to know if the 300-400 ohm to ground it provides would be enough to trip a negative triggered relay, to then open up a direct ground connection for the radio mute?

I've attached a crude diagram of how I plan to tap into the factory wiring on the radio...

Thanks.

Well, I answered this for myself so I will post it up for the benefit of others searching.

For my particular car, I confirmed that the 'voice in' mode (mute and enable voice input) was triggered by grounding the wire on the stereo.

So, I took a gamble and hooked up the "amp control" wire from the F500BT to the voice in wire on my car. Turned on GPS and radio and everything was ok, no smoke yet. Then I hit the round button on the GPS to trigger a voice prompt, and the radio display switched to "voice in" and muted the music.

So, in my particular case, the 'amp control' wire works perfectly to interface with my factory stereo.

Hope this helps someone.

what about the steering wheel controls for volume. DO you think that the wires from the steering wheel controls can be connected to the bt 500/amp. without using that PAC module of whatever its called.

Probably not, though the way I have my F500 wired it plays through the factory stereo, I am not using the F500 specific amp. So my steering controls work.

I am doing something similar but with the ND-G500 amp. I have the amp control wire connected to a special external mute box (a quickconnect QCHBB) which I needed to connect the Pioneer ISO harness to my HU (without having to wire to the factory external amp). It mutes well but sometimes doesn't un-mute immediately (10-60sec delay). I was wondering if this could be due the fact that there is still 0.18V. Do you ever see this?

I was thinking of trying your negative trigger relay and assume it would look something like the "convert a positive output to a negative" as seen on this site:

http://www.the12volt.com/relays/page1.asp

Is this what your were thinking?

Thanks.