Rear Brake Light Sensor—Aftermarket Pressure Sensor
The spring loaded stock rear brake sensor switch works pretty well for activating the brake light but it may require occasional adjustment. An aftermarket pressure sensor may be installed to replace it. A pressure sensor switch is required to retain function off the rear brake light with most aftermarket rearsets.
Adjustment
If the rear brake sensor switch is not responding to reasonable application of the brake pedal, the sensor should be adjusted.
The disassembly pictures below show how the sensor works but it is not necessary to disassemble other parts to adjust the sensor.
The brake sensor switch has a spring loaded plunger that is pulled down by a linkage wire that connects to the rear brake pedal. The switch is drawn closer to being ON or OFF by how far it is threaded into the sensor mount on the back of the foot peg assembly. The brake light is activated with less pedal throw if the sensor is threaded up and more pedal throw if it is threaded down.
Hold the sensor body and turn the plastic nut to raise or lower the sensor. Apply the rear brake to test the response of the brake light.
Be careful to allow some play in the rear brake sensor switch or the brake light will flicker from vibrations or be activated by accidental foot contact with the pedal.
Removal
Remove the seat.
1. Disconnect the rear brake light sensor switch lead. It is located at the back RH corner of the fuel tank.
2. Pull the linkage wire down and unhook it from the rear brake pedal. It is not necessary to remove the foot peg assembly. 
3. Thread the sensor all of the way out of the large plastic nut on the mount behind the foot peg assembly.
Installation
Installation for the OEM rear brake light sensor switch is the reverse procedure. Refer to the Adjustment procedure at the beginning of this tutorial after the sensor is installed.
To install an aftermarket pressure sensor switch, FIRST:
Disconnect the stock sensor lead.
Empty the rear brake system of all fluid. Steps 1 rough 10, Hydraulic System Bleed and Purge.
Remove the banjo bolt from the ring coupling on the rear brake master cylinder. Step 4, Brake Lines Replacement
4. Place a new metal gasket on both sides of the ring coupler. Thread the sensor through the ring coupler and into the rear brake master cylinder. 
Tighten the aftermarket sensor according to your own judgement. The torque spec for stock banjo bolts is 18 ft lbs.
Steps 6 through 9, Brake Line Replacement
5. Connect the sensor lead. I used a zip tie and self adhesive mounting plate to secure the wire to the frame.
* Last updated by: Rook on 1/28/2018 @ 11:27 AM *