omars rear tail light wiring

trying to wire up an Omars fiberglass tail section which included the tail light. From the tail light there is a red and black wire I can only get one portion of the dual element to light. should there not be 3 wires (running/brake and grd) from the tail piece.

Red -Brake, Black -Tail. Run a seperate ground wire to a screw on the bracket.

Thanks a lot, it is now working!!!!!