If you find the plug on the back of the pedal unplug it . If its still on you have a short. To find out where the short is wont be easy but as long as you unplug everything from the brake light curcuit you can test the cables for continuety and have an idea of where the problem is.
Should be something silly tho but a nighmare untill you find it!
Are the rear bulbs stop and tail in one bulb or are they individual?