The rear wiring harness on a 67 coupe generally does go across the driverside rear wheel well. There is a plastic clip on the harness to hold it up over the inner most part of the wheel well and it mounts into a hole somewhere in front of the trunk hinge (I will try to get a pic of where it mounts tonight). More times than not, I have found the harness just draped across the top of the well house and not "clipped" in. Also there is a metal tab in the top of the driverside quarter panel for the harness before the tail light panel.
The fuel gauge wiring goes behind the hinge (in the open space of the trunk) and a clip holds it to the luggage guard. Also 2-3 pieces of gaffers tape holds this wiring to the wheel well/trunk floor.
The routing of the dome light is from the roof center support straight to the driverside roof rail. From there it goes to the B-pillar and drops down to plug into the rear wiring harness. There are a few metal clips to hold this wiring in place on its way to the rear harness. These clips keep the wire from rubbing on the sharp edges.
Regards,
Pete Morgan