I think tmannian is on to it. I have an 05 V70 that had a similar problem. I found that there were two broken wires in the wire harness that runs down the driver side tailgate hinge. This bundle is in a bad position because it is stressed each time the tailgate is cycled. In my case it was obvious which were the broken wires when I accessed the wire bundle. You will have to cut open the braided insulation to get to the wires. It's a reasonably easy task. Good luck!