I think there is power there all the time. Not sure though. Get a volt meter and check for voltage on each of the screws to ground. If both do not have voltage then turn the key on and check again. the one with out voltage is the side you want to use as that is the one that turns on the lights. there are two sets of contacts of the brake plunger.
While your there working in the area, lube up the inside under the pedal plunger to keep it well lubed. Mine was sticking a few month ago and the damn lights kept going on and off. not any more since I lube it. wd40 or pb3.