People! Surely the following should have been addressed before now!
The goal is to trigger an 'action' as soon as the brakes are used, not when the effect of using them becomes apparent (or not).
It is worthy of a thread in its own right! A deep discussion of fundamental Heisenberg issues!!
But to turn to something useful...
Do you need to know how hard/ how much braking? Or merely that braking has been initiated??
If the latter will do....
A weatherproof (your environment IS challenging!) pushbutton switch kludged onto the thing you squeeze to apply the brakes, and held shut (pressed up against some part of frame) when you don't squeeze. When you squeeze, pressure on the button released, "braking" detected!