You may have noticed my comment "long shot" in the post regarding the ground points. I didn't feel that it would fix the problem as I was aware of the ground being used for other circuits. The OP had confirmed that he had checked all of the points that I had made previously and I ran out of ideas. I still feel that he is losing continuity between the driver's door and the pax door.
Looking at the schematics (connector pinouts/ wiring location diagrams/wiring diagrams) in the 2004 Service Manual, it appears that the circuit 294 TN, is for the unlock circuit for the pax door and both rear doors. This wire goes from the Driver's door switch module, connector C1 pin5, to the C202 connector pin 9 at the driver's door hinge. It continues to splice S308, under the dash, where it connects to the two wires to the rear door unlock circuits. From there it continues to connector C211 at the pax door hinge, and into the pax door. It appears that the two rear door unlock circuits split at the splice pack, and go down the left and right sides under the sill plates, to their respective connectors (C316 Lt & C317 Rt) at the hinge areas.
The gray wire that you are not as suspicious of is the circuit 295 for locking of the pax and two rear doors. Obviously, it will run the same physical route as 294 except for the pin assignments (C1=pin4, C202=pin3, C211=pin3). The circuit splices at S309, under the dash, which is where the rear door unlock wiring ties in.
You may also have a problem with the rear door "override" switch that is part of the driver's door switch module.
I don't think that the grounds are necessarily redundant, but I'm getting a headache from looking at diagrams, so this is it for now. Good luck and keep us updated.