I just had a new Sony headunit installed in my Nissan Xterra and there's a slight probelm. The volume only goes half-way before maxing out. The installer said I need some special " wire " or connection piece ($60) to fix it and this problem is due to the make of the car being Nissan. Any other HU would have the same result with the volume. If I was to install my amp and sub right now when adjusting the sub through the HU the other speakers would adjust with it. At the time the installer didn't know the name of the part I need but he did know it would cost $60 for the part and $20 labor.
Any idea what part I need?