'91 Shadow no brake lights when headlights are on??

This is a very strange problem, my brake lights work completely fine until I turn headlights on, still have my tail lights and signals but no brake lights? any idea what can cause this?

Could be poor grounds.I had a similar issue on a Shadow I had back many moons ago. If I remember correctly I ended up just hard grounding all the taillight ground wires to fix my issue.

Find your brake light switch by the brake pedal check for power to the switch. If it has power check if the switch is working.

Find your brake light switch by the brake pedal check for power to the switch. If it has power check if the switch is working.

HAha tranny crapped out before I ever figured out this problem.