I also called crutchfield and in there documentation it says to leave it, as it is a signal wire that must be connected. (Says guy on phone)

But that just tells me, they don’t know what it is either.

Pulling the amp fuse did nothing to effect functionality of the car. Still drivable and could still start. Radio still functioned without sound. Sirius XM still displayed channels. Onstar mirror still had green active status light.

Seems like no one else has removed the factory amplifier?

So the only thing left to do is, voltmeter the signal, cut the wire, and call onstar after wire is cut to see if they notice anything and confirm the voice call with them still works while listening to the radio first to check mute functionality while on call.

Doing this will answer this question not just for me, but for anyone that doesn’t want to look for a junkyard amp later down the line to keep there HHR functioning properly when there is a problem with the stereo. We are just lucky it’s not as complicated as some of the newer cars. We just need to crack what this one wire is!

Hey, isn’t there an option for the premium sound system with XM radio and no Onstar?

That seems to be an option on crutchfield.

If so, do you have all possible schematics?

lol will do.

No mute happens at the radio, the signals are then passed through the radio to the amp, while what ever you were listening to at the radio is muted.

But you never know, I will get to the bottom of this and let you know. Maybe tomorrow, all depends if I feel like taking the car apart or not.

Solved!!!

After cutting the green wire, XM radio, AM/FM radio and onstar still worked.

But I noticed after something would trigger on the amp, either the radio or blinker, it would just stay on with the constant tweeter hum.

So I spliced it back together and bam, the green wire tells the amp to shut back off while not in use.

Pink wire makes it turn on, green wire keeps it off.

Luckily, power completely shuts off when you remove the key with the vehicle off, incase you leave the green wire cut.

So The pink wire must be connected to the accessory position of the key and the green wire just saves power by shutting down the amp when not needed.

If someone has had any problems just using the pink wire to power on your aftermarket amp, please let me know.

Looks like I can use a NC SPST (normally closed single pole single throw) relay and utilize the green wire to save power to the aftermarket amps. Do not connect green wire directly to relay, you will need to convert the digital signal in order to not mess up the output from the radio possibly with a motor driver type chip.
Or maybe a solid state relay will work.