True, it's unlikely but a quicker test than dismantling the starter. An even quicker test, when the engine starts but the lights remain off after releasing the start button, push the start button a number of times. If the lights then come on, that's looking like Laitch's path is the one to follow, if there's no change with the earth jumper test.
Unlike a lot of bikes, it's OK with a brick to push the start button when the engine is already running.