Sendo,
The harness runs from each sidewall out through the cutout in the lower trim bolster, across the floor (under the rear seat cushion) and merge into a long multi-wire bundle that runs forward under the rear carpet section and then under the front carpet section, exiting at the fire wall and continuing up to connect with the front harness under the dash. The photos below show the rear harness on the floor ready to be threaded under the carpet sections. After unbolting the front seat belt retractor, the rear carpet section was easy to just lift and pull the wires up along the transmission tunnel on the driver's side but the front carpet section was held in place by the console so I used a broken shovel handle to push the connector (taped onto the broken end of the handle) with the rest of the wire underneath the front carpet section along the transmission tunnel, coming out at the firewall. Then, just pull the harness straight under the carpet and feed the connector up to mate with the front harness. I hope you can see from the photos below how I did this, although there are probably other ways to do it.