The orange is the power wire - there are 2 of them taped together, one powers the brake lights, the other powers the roof light. One side of the stop light switch goes in here.
The black wire is the tail light wire.
The stop lamps run through the indicator wires, ie the pink and purple wires, but after the power goes into the column and through the switch.
UNLESS you have a late FC with separate orange indicators at the rear. Then the stop light switch goes to the wire which runs to the same rear globe with the black wire in it. Does this make sense? It's much easier just pointing to a wire and saying "this one"
Ken