I'd probably want to make it as small, and unobtrusive as possible. I think I'd rather rig up a small LED and place it behind me in such a way that the camera sees it, but I don't. Nothing more distracting than diving into turn 1 under brakes and see a red light near the dash. Even if I know what it is...
I'm sure others have their own philosophy about dash instrumentation. But for me, on the track, I wouldn't want any lights going on or off in my field of view unless they're lights that are telling me something IMPORTANT.
How about a small red LED for brakes, and wire up a bar graph LED to a Throttle Position Sensor on the throttle shaft. Then you've got telemetry!!!
-Josh2