[davepl]

If I put a switch down at the pedal mechanism could I not tie it directly to the brown Brake wire? I mean I don't even need a diode because I don't care about backflow, it's just a switched ground.

This seems like such a good and simple idea but I've never heard of it being done.

If wired like this you'd still have your hydraulic warning but you'd get a "you left your parking brake on" light as well (same light).