The footwell carpet covers the switch, so it's really neat.

Next I measured and cut the underbonnet end, soldered the ends and fitted the plug. Then threaded the wire through and connected it to the switch loom, securing with cable ties.
This is the hydraulic switch with relay cables and microswitch cables.

And this is looking down - offside. You can see the chassis rail and a hint of the red wires. The plug connector is just to the right.

And this is a reminder of how I mounted the relay. It hangs on a bracket from the cross tube. You can also see the hydraulic swich at the bottom of this shot.

Finally, to smarten the grommet up, I've added a shaped strip of neoprene with a cable tie. Compare this with the earlier photo, it's an improvement.

I've tested this system all the way through, and the microswitch gives an instant response, which means earlier brake lamp activation.