Tail light ground

Noticed that my driver side tail light was illuminated with the ignition off. Car was going to be sitting so I pulled bulb and left it. Came back several days later and battery was dead and passenger side reverse and brake bulbs were both blown. I've replaced all bulbs and the fuse and followed wiring from back to panel. Where do I need to hook a meter to see if I have power and where are my grounds for this wiring system? Don't know if I have a bad groud. Side note, just replaced master cylinder and had brake pedal unhooked. It's hooked back up but is it possible that the brake switch on the pedal is adjusted wrong or fouled up altogether and is draining my battery? I currently have no brake lights or tail lights. Thanks