Sorry Chappo I probably didn't explain myself very well.
Most OEM rearset have a little micro switch which is connected to the brake lever by a small spring, so when you press on the brake lever with your foot the switch is activated and the rear brake light comes on. When your foot is removed from the brake lever the spring returns the lever back to its original position, the switch then reverts back to its original open circuit position and the brake light goes off.
Most aftermarket rearsets do not have this facility to use the oem brake light switch as they are primarily designed for race use so a brake light and subsequently a brake light switch is not needed. To get round this lack of brake switch when using aftermarket rearsets on a road bike you fit a different bolt through the banjo fitting located at the master cylinder. This different bolt has a pressure switch built into it that is connected to the brake light, so when pressure is built up in the hydraulic brake line the switch is made and the brake light comes on. Reversely when pressure is relieved by removing you foot from the brake lever the pressure switch goes open circuit and the brake light goes out.
Looking at your photo I cannot see a pressure switch bolt holding the banjo fitting to the master cylinder therefore I'm assuming your particular aftermarker rearset design utilise's the original design of a micro switch connected to the lever by a spring. This arrangement in aftermarket rearsets is rare and the only model of rearset I know which incorporates the original micro switch design is the Gilles VCR.