Oliver;

...a minor point, but since the (OE hydraulic pressure sensing) switch supplies (ign) power to the brake lights (unlike typical automotive control circuits where they like to make a connection to the vehicle chassis thereby saving one wire), if you look carefully at that OE switch, you will find not one, but two wires connecting to it (a Brown one supplying power from F2, and a Red one running off to the lights at rear of vehicle).

For reference, check wiring dia: http://www.intelab.com/swem/122S%20Wiring%20Diagram.jpg [Look for item No 19]

Cheers