If you are running new wire, go ahead and add a ground wire to the harness. Its will save you some headaches down the road when each light is grounded right in the cab where you can get to it. Also, wire the stop-turn lights with green wire on the right, and yellow wire on the left. I like using heavier wire so I know I have plenty of current and voltage, 16 gage is what I would use.
Doing it this way, you would have four wires running to the rear,
#1 tail lamps (brown wire)
#2 stop-turn left side (yellow wire)
#3 stop-turn right side (green wire)
#4 ground (black wire)
Optional addition
#5 back up lamps (blue wire)
Joe
