I have a new to me avid d3. I want to do the e-brake signal wire bypass but i don't have a mute wire coming off the back of my radio. Is there anything else I can do?

You can probably connect that lead to power then to a switch then the other side to where you would have connected the mute wire.

Then you flick your switch instead on pressing mute to send the signal along as if it came from the head unit directly.