The localizer demarcates the center line of the runway, and is used to indicate horizontal deviation on the CDI at the bottom-middle of the HUD.
It is not the red cone. The red cone is a visual aid put on the map and mini-map in IF. Nothing more.
When told to maintain 180 until established on the localizer, say, for runway 15, this means that as the CDI nears the middle line [slight clarification: in my mind I was thinking “when the line stops blinking and begins moving toward the center”, not as @MJames pointed out, just before it hits the center, that would be too late], you should turn to runway heading so that you are aligned with the center line.
It does not mean you continue to fly 180 until you hit the cone. The cone, again, is a visual aid, not part of the Instrument Approach.