On opening my controller there is a small PCB under shrink wrap that appears to be connected to the lighting output. What is on that PCB is a mystery but I am guessing the transistor you mention.
My idea was to use the light output wire as the low voltage side of an optical relay as per the ES thread I linked above and use 12v from a DC/DC converter to power the lights. As I want to also be able to ride my trike with the motor wheel removed the lighting circuit will optionally be powered by a 3S 5000 mAh Lipo brick.
Projected are:
- always on head and tail lights
- brake light, nothing fancy, just a second rear LED light that is turned on by the brake sensors (possibly mounted high up for SUV's...)
- indicators, mostly useful in "warning" mode - all flashing for riding in town where there are no cycle paths but a motorcycle turn signal, switch will be mounted too
- hi/lo beam headlights, again nothing fancy just a second headlight adding 70-80 lux when on the open road. This is the one I want to be able to turn on from the controller button.