I, too, am about to add a CD changer to my '93 volvo, and to the best of my knowledge there is only the one data cable. Go to www.crutchfield.com. That's where I am getting my adapter. According to Crutchfield, all i need to install the CD Changer is an adapter. The website says nothing about the need for an additional power cable. So if their info is correct, that is all you should need. Crutchfield is also including installation instructions with the my adapter. Crutchfield has instant online customer support, so you might want to try to ask them directly.