your diagram shows a single wire (vio-blk terminal "p" of the bh connector) going to the rear lights connector and a single white running to the connector to the underdash turn indicator switch.
I'm not sure of your nss, does it have 3, or 4 wires. The body of the switch itself may be providing the ground. I can't recall if you are using a new nss, how many wires in it's connector. I believe it's 3?