The rear light harness connects just near the emergency brake area. It goes back under the sills and then continues onto the trunk. At the rear seat, before going into the trunk the dome light harness connects and then goes up the inner sail panel.
Try the easiest first, do you have power at the rear lights? Then move onto:
1) Remove rear seat
2) You may have to remove the rear panel on the rear driver side to get to the connector (maybe)
3) Unplug the connector and see if you have power.
4) Trace the power problem all the way forward to the emergency brake area.