I want to solder in a Bluetooth dongle into the FM pre-amp channels on my stock head unit. The board does not have the L/R channels marked like usual as far as I can tell. Problem is now we can't get the radio to unlock without the steering wheel mute button. Is there a way to unlock the head unit while out of the car? If so then we can use a oscilloscope to find the left and right channels on the board to solder into.