If it worked previously post ABS removal, try some contact cleaner & exercise the microswitch beneath the lever. Otherwise check the connector (under the right side of the tank IIRC).
Rang Motobins who were scratching their heads not sure which one. Motorworks the same however Motorworks are sending both types one new and one second hand. Which ever one doesn't work can be returned.
When I squeeze the lever it releases the spring switch illuminating the brake light.